KT if you have a method of testing a girl, by all means stick to it...after all this girl did accept your 20 to kiss you. Some other girl may tell you to fuck off...and am sure many have, if you really try this with everyone.
In my view you offered this girl 20 to kiss. She accepted and you kissed. What makes this completely unacceptBle however is thT you snatched the money back from her after kissing. Thats the equivalent of you fucking her and not liking it, snatching the money back from her.
Its not done, is illegal and bordering on molestation.
If you keep doing this (ie snatching money back from girls after the service agreed to is availed of) there is a chance you will end up in jail....or worse, roughed up really badly by a girl's pimp or security.
In my opnin you should have walked...but left your 20 with the girl.