1) The ebay bubble has burst. This is a combination of the novelty factor wearing off and it has reached saturation point. I remember the days when you could get a new product in and sell out within a few days/weeks.
2) Ebay is broke. There are so many thing not working and the new search has broke
3) Yes there are many sellers leaving. Not bedroom sellers, 30K+ feedback sellers. Why? Because you list and items don't simply sell, not because of the changes (although that has contributed also). Whats' the point paying 2 or 3 grand a month in listing fees if the stuff is just rotating without any sales? Prime example, we can list the same product 4 times a day for maximum exposure. 28 listings a week and be lucky to get one or two sale of that item.
4) You can not leave feedback on Amazon. But you can not compare Amazon to eBay. Ebay customers are pikeys shopping at a car boot sale. Amazon customers are decent understanding people who are not so price conscious shopping at John Lewis. They pay the price, they pay the postage and job done (sometimes they even leave feedback!!!!

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Yes ebay is over. The good days are over. 2 years ago we could comfortably sell £40K a month on eBay. Very busy, smaller margins generally when compared to retail but a very a steady income. Now we are looking at a third of that on a good month (although we have been dropping stuff since November).
Yes ebay will always be there. Yes there will always be buyers and sellers. But you will find it increasing difficult to make a living on there.