Well, yes. Any spell can backfire.
And I recommend not to do a love spell. They control people's will, and in some cases harms them. Using magick to make someone fall in love with you is lying to yourself and totally playing with the other person's emotions. I've even heard of a case where a female witch did a love spell on a guy, then she fell out of love, but he didn't (because of the spell) and then he raped her.
agreed you should never do a love spell as sara said it is (if for u) self gain and any spell within the craft for self gain is not accepted or recognised and if it unrequired love in which case it will be can backfire badly i strongly advise u not to do this. remember what is sent out comes back three fold.
if for someone else you should tell them u are unable to do the spell and give your reasons why, it may backfire and the preposed spell could come back to you !
blessed be