Hi Andre, I have had many interactions [100% positive feedback], both selling and buying, and almost all have been positive . The 95 - 98% positive experience rate mentioned above is about accurate. My perception is that you should be more patient, at least in two cases:
Winning bidders who don't establish communication within 48 hrs after winning an item, against terms of the listing. Think about somebody out on vacation or on a business trip with difficulties to access safe web sites.
Winning bidders who don't make themselves available to sign for their UPS packages in order to facilitate closing the deal. Think about people working all day who aren't supposed to receive private packages at their work address.
Ebay has become such an everyday part of business that at least I have made allowances for people who have a life outside of ebay.
Interactions with foreign countries have a slightly higher problem rate. But from time to time you might find an Asian bidder willing to pay a collector's price for an item that will fetch much less in the US. You might open up items that might be viewed as such to foreign bidders as they may increase your profit by several hundreds or thousands of dollars.
Anyway, just some thoughts. Good luck in the future.