i have been with this panel, findparticipants, for a few months. so far i have been invited to 3 studies, one being completely voluntarily and the other 2 involving a raffle/sweeps for the incentive. so obviously not ideal but since the amount of participants for these surveys is probably low your odds are much better winning a prize here than with some of the other big name sites. that being said, i haven't won anything yet :(
that doesn't mean there aren't any paying sites here, their site says there are, i just haven't been invited to any yet. nevertheless, it is worth the signup just to see what comes your way. if anything else, i find research, more academic-based surveys are far more engaging and interesting!