What is to keep a scammer from becoming a supporting member? If your potential take is $1500, what's a minor contribution?
Heck, even legit bass players have pulled crap here, so what is excluding folks based on financial outlay going to accomplish?
Implication being the non supporting members are dishonest?
No, but a scammer is not likely to pay money to TalkBass.com because it leaves a trail. It certainly wouldn't be a 100% failsafe solution, but in my understanding a hurdle like this can be a big deterrent.
Waiting 30 days or so could also work, but may create confusion as the user wouldn't know when he'd be able to start seeing threads in the Wanted forum. He/she may just assume there are no threads there.