It is nearly impossible to imagine a legitimate reason why a seller if he has received the money hasn't either sent the goods or been at pains to advise the buyer why there is a delay. If said person is present on APUG it sort of rules out disasters like family bereavement, detention in police custody etc where communication is impossible or beyond the state of mind of the seller due to the circumstances he/she fins him/herself in.
On e-bay there would presumably already be a disputes procedure where e-bay whose business it is to facilitate selling and buying has a vested interest in protecting buyers.
APUG relies on a form of goodwill and has few real sanctions when deals go wrong unless someone can tell me different.
Once that goodwill goes then APUG classifieds will be classed as less safe than e-bay. Maybe the sheer number of subscribers now means that the risk factor is such that we can expect to see more problems in classifieds.
Not a good state of affairs