I suggest a minimum post count to make posts in the classified sections.
It's certainly been given thought although I'd suggest that someone intent on scamming (as opposed to be a bit crap) would get round a minimum post count easily enough within half an hour (or the minimum post count would be so high as to dissuade genuine sellers with few posts).
Rules suggest that nobody should pay by gift
It should be banned as a payment method, it isn't like it stops you paying via paypal "goods". That way, no matter what is sold, the recipient if unhappy for whatever (valid) reason, will be able to follow this up with paypal.
Paypal is a third party site so not sure how a particular type of transfer can be 'banned'.
We can only recommend and the responsibility for type of payment lies with the buyer - if the seller will only accept a Paypal Gift then there are three choices for the buyer 1) pay the fees themselves; 2) pay as a Gift and take the risk; 3) walk away. Which option the buyer chooses is up to them but the guidance from the site is clear about not using Gift payments.
Bottom line is that you can use Paypal (as a gift or not), bank transfer, cheque, Western Union or just stick some cash in an envelope and hope for the best. I know how I prefer to pay, and not only because I managed to get myself a real steal of a deal on 1,000 lightly used manilla envelopes.