Duncan,
I think it is always the seller who sets the terms of an auction or buy it now listing, and the buyer who agrees to those terms by bidding or buying. These terms, of course, should conform to
ebay policies and should be known up front, i.e. stated in the listing.
For example, if I have terms that say that payment is expected within a certain number of days, and have my automatic functions set to open
an unpaid item case after that, well, shouldn't the buyer know and expect that going in?
The larger question is just as you posed it - should a seller wait three weeks for a payment? To me, it is ridiculous for a buyer to assume that they can be a slow poke on the payment side WITHOUT prior communication with a seller. That is way too long...
Communication is the key. Buyers have a very clear obligation to pay for lots won - especially if the seller terms are clear on this point.
If I did not have specific terms for payment, I would send a polite email through the
ebay system after 5-7 days, asking if they were done buying and when they planned to pay. If I did not receive a response to this inquiry, I would not hesitate opening an item not paid dispute. It isn't a personal thing at all, and
ebay will change any negative received based upon non-payment.
All of the above are my not so humble opinions...
John