Charles,
I have made numerous purchases on E-bay While I don't use Paypal I like to insure my sellers that their monies are forthcoming the next best way which is Postal M.O.
Generally once an auction ends the purchaser has 3 days in which to contact the seller. If payment is sent out on that third day, dependant on the postal service and what part of the country payment is coming from, I would allow a good 14 days before I got nervous. That is of course if payment is sent out as promised.
I also agree with Rich that trust should be a two way street. The burden of trust should not always be left on the buyer since there are non-reputable sellers also.
Feedback while not 100% foolproof should give you some indication as to the character of the person you are dealing with.