Personally, the "safety" of a spirit depends on more than just assume that the identity of a spirit is the final factor. For me, there are 3 criteria to consider:
Respect:
Others have already mentioned this, but it deserves repeating always. Treating the spirit with respect and consideration get you quite far. You just need to consider the different approaches used in calling the Goetic spirit. The first one is the original method from the Ars Goetia, which uses incantations that demand, curse, and threaten the spirit to show up. While the spirits are not human and should be treated as such, this attitude will infuse an adversarial energy into whatever shows up and maybe it might not be dangerous in the moment, but it may most definitely screw up your results or add an unlucky twist into them.
Now consider the opposite end of the "respect" aspects in demonolatry. Reading the works of individuals such as S. Connolly, you will see that worship, adulation, and even supplication are used in their methods to communicate with the spirit. For some, this can work and you can certainly try it if you want. But the main issue with this form of excessive respect is that these currents invite the spirit far too much into your life. Your energy may co-mingle with theirs more than you want and this can invite their presence beyond the boundaries that you are comfortable with. However, this is more a matter of my opinion rather than objective truth and so this is far safer in my eyes than the grimoire method. You can get safe manifestations and results through this type of approach.
Finally, you have the middle ground of respect, where you neither command nor worship. It is promoted in books such as "Demons of Magick" (DoM) by Gordon Winterfield and it is the one I agree with the most. DoM insists that you position yourself as being the respected authority figure to the Goetic spirit and you make you respectfully request your results with the divine authority granted by the ritual method. You treat the spirit with respect, but you are the one who wields the correct amount of power in the interaction. For me, I like this approach, but I also think it better to treat the spirit as an equal. I know I have the power and authority to use if necessary, but I would rather make my request respectfully and then outline the terms of our transaction. Then I assume agreement (since I am not clairvoyant) and give license to depart so that the work can start. I am respectfully transactional in this sense and do not believe in considering spirits "friends". For me, results have either worked wonderfully or nothing happens; I have never experienced true misfortune by adopting this attitude. For me, it is the best approach and the one I recommend.
Method:
As A.Nox mentioned, the method can provide much to a safe interaction with a Goetic spirit. Respect is often built into the method and you will see this with the various approaches I will underline. It is always a good idea to use the grimoires as a starting point to understand how the methods have evolved to become safer.
In the original Ars Goetia, you use an assortment of divinely consecrated instruments, divine names, and conjurations to work with the spirit. Items such as the lamen, the hexagram, the circle, the ring and the triangle ensure you are protected against the spirit by providing warding and boundaries. Elements such as the sword, the lions belt, and the increasingly severe set of conjurations provide you the threatening authority to command the spirit. Finally, all of the purification, prayer and fasting provide you the clarity and purity necessary to wield the command and communicate with the spirit. Inside of all of this mess, you will see that the entire method is relying mostly on you assuming you are god and using divine names + symbols as a safety measure against the spirit. In other words, beyond "god", you are truly the only one dealing with your own safety.
Going to Dr. Rudd's version of the Goetia, you will see that a "thwarting" angel is added into the mix to bind the Goetic spirit. This is also used in DoM, along with angelic emissaries connected to the binding angel. The angel adds counterbalance to the spirit's presence and also adds an element of control to the demon's power in manifesting your result. Research online for those who have used this approach and you will see that many noted the binding angel to help "quiet" things down a lot and make the process smoother. In my opinion this is an important safety mechanism that helps to provide a large aspect of safety to the operation of you are not going with a demonolatry approach. It is my preferred central mechanism along with the so-called "middle ground" approach to respect I mentioned above.
On the subject of DoM, the book's method also adds 2 things to consider to help things out. The first is imaginary "evocation keys" that are sensory imaginations you use to fill the astral atmosphere of your ritual space with sensations unique to the spirit. I have tested with and without these keys to see the difference and I find they help in aiding manifestation of the spirit. In my eyes, it not only helps the spirit manifest, but also adds into "respect" built into the method. The 2nd element is offerings as payment to the spirit for its labour. An offering is a sign of acknowledgement and thanks to the spirit for its work and it is showing you recognise it as a partner in your interaction. It is also a battery source for the spirit to use to help anchor your result into the physical world, which aids manifestation of your desire. These signs of goodwill add to the sense of safety that a method can give you and are worth considering.
The final aspect of method I want to consider is that of demonolatry. As I said, demonolatry verges on worship, communion, and adulation for the spirit. Again, nothing necessarily wrong with that and it works for a lot of people, but there are some considerations you want to think about here. In a lot of rituals of demonolatry, a common practice is to invoke the spirit directly to you or inside of you. If not that, then a lot of these methods simply involve calling the spirit to you without any control valves or boundaries, producing "loose" methods of contact. One thing I found in my own time working with spirits, is that their energy can leak into you and intermingle with you. This can, at least temporarily, affect you on a psychological level. It is common in direct invocation to assume characteristics of the spirit you invoke into yourself and this is one distinct thing that happens a lot in demonolatry. Personally, I am not a fan of mixing my own energy with a spirits and can have implications to your psychology (positive or negative). If you are not a fan of this or fear this issue, then the methods of demonolatry are not classified as "safe" in my eyes when you engage with any Goetic spirit. This can apply to any spirit however.
The Spirit's Identity
Finally, we arrive at the spirit's identity in considering safety. If you consider a common definition of what a spirit is, then we can define it (very roughly) as some sort of amorphous blob / field of energy that has a sense of intelligence to it. This blob of energy has its own character, set of abilities, and composition that makes it unique from another blob of energy. What this means is that every spirit has its own identity and this can have implications for how "safe" it is. The big question is how you assess that "character".
The old grimoire descriptions of spirits are often a good place to start and further research into the experiences of other practitioners is always helpful. Going by the Ars Goetia, spirits such as Glasya Labolas and Andras are dangerous because the grimoire specifically states them as either being an "author of bloodshed" or killing the practitioner and their relatives if improperly evoked. Online research from others show statements that either support these natures or depictions that show these spirits are more "serious" compared to other Goetic spirits. On the other hand, the same grimoire mentions spirits such as Vassago and Orobas as being "good natured" or "faithful" to the practitioner. My own experiences with Orobas have shown this and online depictions of Vassago support the good-natured theory. So from the grimoires, we could at least assume that the grimoires give guidance into how safe a spirit is based on its identity.
You can also take the spirit's abilities as being extensions of their personalities. For example, "Andras" is considered a spirit of discord and causes discord among others. So it is fair to assume that discord and chaos are sort of built into the spirit's personality to some extent. If we take a look into a spirit such as Belial, then we see it grants renown, power, and prestige. We can assume that power and renown are also a part of Belial's character. In all of these cases, we must consider how such personalities can clash with a practitioner. Depending on how these characters interact with our own personalities, we might experience a wide range of responses from these spirits. This can range from simply refusing to work with us or to actual misfortunate consequences in our results (ie "bad luck").
But ultimately, I will say this on how the spirit's identity affects its "safety". You cannot know for sure if what you call will correspond precisely with what others have experienced. For example, Orobas is experienced as safe and helpful in my experiences, but it turned a friend of Lon Milo Duquette into a horse gambling addict who overturned his own life. Your own experience will likely be unique and your research into the spirit's character can only take you so far before you experience it yourself. This is why you maximise your chances for safety by considering a good strong method and an approach marked with respect to the spirit. These 2 other factors will apply to all spirits and then you will never have to make a bet on its character being safe or dangerous. You will be able to discover the character of the spirit in a safer and secure way.
My conclusion (ie TLDR):
The method, the attitude of approach (respect), and the identity of the Goetic spirit all determine how "safe" it is. You want to have a good method and a respectful attitude towards all spirits in order to ensure you have a systematically safe approach to working with them, regardless of their characters. The characters and abilities of a spirit can be considered safe or dangerous to different types of people and this is also something to consider. What kind of person you are and what is the spirit like? How will you intermingle with something like that? This is important, but you can always decrease that risk by adopting a good set of secure protocols to working with the spirit and ensuring you do so with respect.
In all my experiences with Goetic spirits, I have not gotten truly dangerous results or manifestations with any of them. I have worked with around 20+ spirits and all of them have been great without any real problems. I did get some "bad" results that turned out to be me in need of lessons, but I do not attribute this to the spirit and rather to my own immaturity. I hope these considerations help you.