The movie was made around the 80s or 90s and it is about guys paying a guy to go out with a girl who isn't very popular but has a bad girl reputation and he has a bad boy reputation , just so one of the other guys can date the girls sister, because the rule is that she can date when her sister dates. But the guy ends up falling for the girl.

Sounds like this:
10 Things I Hate About You (1999) - IMDb (http://www.imdb.com/title/tt0147800/)