What BigMat and 71chebby said. On another forum we jumped from 50 to 100 and it seemed to work good. You could definitely weed out the bullshit posts and it really deterred those with no desire to do anything but sell.

50 definitely worked better than the 15 does here, but the switch to 100 would completely kill the for sale section like it did on the other site. It took us a good month or two to get the for sale section up and spinning again.

I voted 75 for the above reasons.