[iggymcfly]

The thing is that if he's drawing on the flop, it's almost impossible for the offsuit 3 to improve his draw. If he's bad enough to do this with a set, then go ahead and raise, but against a decent player, this will almost always be naked QJ. Really, you have to go with some sort of read here, even if it's as simple as "there tend to be a lot of huge donkeys on this site that will pot the turn with less than QJ".

If you think there's a reasonable chance that he's got one of those hands (> 15%), then you better just repot it. Against a decent player, this is a great spot to call and bet any scare card on the river, as such a player will have naked QJ > 90% of the time and some kind of weak redraw like AQJ3 if he's got any redraw at all.