The main thing I dislike about eBay search is all the sponsored placements violating the sorting order. For example, if you sort on increasing price, sponsored placements not in the specified sorting order litter that heavily, making it hard to follow. Amazon searches have the same problem. (Problem, from the perspective of buyer-on-the-marketplace.)
The other thing I dislike about both eBay and Amazon searches is the spamming of huge numbers of listings for essentially the same item. I notice it more on Amazon than eBay.