I've been selling there for about a year, though I'm not really very high volume.
I did have to do one refund, the customer bought a new item that didn't work, after a few emails and his contacting the manufacturer's tech support, he sent it back (he paid shipping) and I refunded his money.
I *think* that Amazon is a little more seller-friendly than PP, though I've never had a dispute.
The only bad thing about Amazon marketplace is their relatively high commission charges--I just sold a CD, priced at 29.99, after shipping credit (which is fair), commission, postage, and listing fees, my net is about 24.50. You just have to take that into account when pricing your items, and I'll admit, I sell things for more than I'd get on Half.com, and much easier than ebay.
Actually here's an interesting read about this:
http://www.amazonsellercommunity.com/forums/thread.jspa?messageID=1524705&tstart=0#1524705
lots to read, but they suggest:
1. Ship promptly and use a shipping method that ensures reliable delivery before EDD.
2. Ship with tracking information and provide this information to the buyer.
3. Ship higher priced items with signature confirmation tracking and/or insurance.
and of course the fine print:
We reserve the right to seek reimbursement from Seller if we, in our sole discretion, decide to reimburse Buyer under the terms of the Amazon.com A-to-Z Guarantee, provide a refund to Buyer if Seller cannot promptly deliver the goods, discover erroneous or duplicate transactions, or receive a chargeback from Buyer's credit card issuer for the amount of Buyer's purchase from Seller.
however, I think automatic chargebacks would fall under 'buyer abuse', they're supposed to use the Amazon A to Z guarantee.
