The criteria for me is generally how well the shop pays and where the purchase is made.
The highest amount of money I've ever spent is $550, and I knew it would be credited back to my card quickly, and without hassle. Conversely, I did a $75 purchase and return mail order shop, and between the return and reimbursement for shipping costs from the MSC, it took almost two months to be credited. The latter is the shop I wouldn't do again. I am doing another mail order shop next month, but it's for a well-known retailer (the other one was a small operation).
This past month, I did ponder a P&R with a very expensive purchase, but decided that it wasn't a good time for me to incur an unnecessary charge, despite the fact that it would have been credited quickly.