eBay says this:
"Leaving feedback

When should I leave feedback?
Leave feedback after completing any purchase or sale on eBay. Your honest feedback shapes the eBay community and impacts the success and behavior of other eBay members. "

Although on virtually all relatively small auctions, I (as a seller) leave feedback first, there is nothing wrong for the seller to want to leave feedback last. It is normal to fear negative feedback; a seller is not a crook to fear it. And the seller has every right to be concerned that the buyer is happy or not with the purchase. The eBay guidelines above say leave feedback after the purchase or sale is completed. It is only completed when all are happy. The CCGTC Club guidelines, I believe, say all must be happy with a transaction through the mail and the parties can return the stuff and money if not happy. Even if there is no such CCGTCC guideline, it is the way virtually all mail transactions are carried out.

(More in my other post below.)

Robert