What is it with eBay sellers that they think everybody owes them something?  As an occasional eBay purchaser, there are two extremely common practices that are totally unethical and unacceptable:

1. Mandatory delays before shipping an item: Today i received an email from a seller confirming that he had received my payment and that he would ship the item in two days.  Why?  I've already paid for the item - the money is sitting in his bank account.  How is there any excuse for not shipping an item immediately on payment?  The item should be ready for posting when it is listed, or at least as soon as bidding is closed.  If i buy an item in a store, i expect to be able to take it away with me straight away.  As an eBay customer, how am i entitled to less?
2. Sellers insisting on positive feedback before they will give you feedback: This is an even bigger farce.  As soon as i have paid, all of my obligations as a buyer are completed.  If i post bad feedback about their packaging or the quality of their goods, that doesn't make me a bad buyer.

I can't do anything about the first problem, but in the case of the second problem, i just don't give feedback to eBay sellers who don't give me feedback first.  I don't think it's going to really change their behaviour, but it can't hurt.  No seller has rejected my purchases because of a low rating (i think mine is about 42 at the moment), but they seem to prize their own ratings highly.

I think this stems from a basic misunderstanding of what eBay is: many people see it as a way to sell stuff without being a professional seller.  Sadly, many people build eBay businesses with this still in mind.  This is fuzzy thinking - if i buy a CD from K-Mart, it's up to K-Mart, not me, to make it a good transaction.  The same should be true of eBay.  I'm still buying a product or service from them, so i'm still a customer, and the rules of retail sales still apply.