The idea to employ love magic against a specific person is often born by desperation when the person planning to use it can't think straight anymore, is unable to correctly gauge the situation, and recklessly prepared to make any sacrifice to achieve his or her aims. Frequently such attempts are extremely heavy-handed (see Louvre Doll & PGM) and designed to blast through obstacles where none exist in actuality, or are at least not as formidable as they seem. Love spells are most often about possession, not seduction. The aim is to win control over a person, everything else is secondary. "If only I could have him/her, I'd be finally happy!", that kind of illusion.
Blowback can come in the form of obsession. Without a love spell, you may meet an even more interesting or desirable person but once it's been cast, chances are you'll develop tunnel vision and be like on hot coals the whole time, anxiously waiting for any small sign that your magic has worked, failed, may begin working, etc. while life passes you by. Anybody who's ever been in a doomed long-distance relationship will agree - it's as if other potential romantic partners didn't exist.
It's really better to conjure for success in love in a general way, for becoming more attractive or charming, else you might miss out on more suitable candidates around you.
