Flopped a set, but wait now theres a three flush.

[gomberg]

This is a terrible line IMO unless you have a great read. This player is giving you odds to hit your draw with your 2nd best hand at the moment, and you want to reopen the betting? Much more profitable to call this bet and hope the board pairs, then stack against a loose player who can't fold a good hand, all for the measly price of $30.