I had started to address this in the other thread, but it really didn't belong on the BOI.
Variations of this idea have been presented in the past, and the basic fault is that it detracts significantly from the desirability of this site to new members; so the negative impact far outweighs the potential benefit. I don't like that it is easy for somebody to access the classifieds and try to scam our members (including me), but imposing restrictions such as extended time or post requirements would simply lead to people going elsewhere.
Paid classifieds actually cut back significantly on the scammer activity, not just because of the required payment, but the process made it more difficult to set up an account under a false name. That system wasn't perfect, but we didn't have to constantly be on the watch to try to catch the next incarnation of known scammers. Obviously, with the more devious methods utilized by one of the recent problem children, the required payment wouldn't be a hindrance, since the account could be set up to match the cracked PayPal info.
I'd love to have an arsenal of ways to thwart scammer activity, and keep them off this site; but we can't drive away all the other new members in the process. Besides, a dedicated scammer will find a way. Six months ago, how many of us would have thought about people purchasing access to established (positively rated) Ebay accounts , or cracked PayPal accounts. The methods used are getting better, so we have to be more careful...but how many times to we hear about people sending payment without getting, and verifiying, basic information (full name, address, and phone). References are often a joke, but you should check them - nobody is going to give you the name of somebody that will say they are a low life POS...but they might give you a name you recognize that has never dealt with them. If all the references are local, they could just as easily be buddies/partners/aliases.
It's a tough time on both sides: as a buyer, I'm less likely to give a new name a chance - preferring to stick with people I know I can trust...but we're all new sometime, someplace. Not having a recognized name, reputation, or list of solid references doesn't mean somebody doesn't have what they are advertising, or take great care of their animals.
(I've been rambling....you get the idea)