I'm tempted to say that the thing I dislike most about ebay sellers, is that
they are using ebay to sell

. However, that snide response dodges the
intent of the question...
I used ebay consistently until the early 2000s, then it fell out of favor with
me due to the standard reasons people often cite- which are profound
enough to have driven me away by themselves. The biggest
issue about many ebay sellers for me, however, is that too many have
"flipped" basic selling concepts on their heads, to make it easier on
themselves. Too many think the idea that "the customer is always right" is
somehow absurd or profane, for starters. Some sellers answer a specific
(and common) question about a card by replying "I don't know much about
cards" or "I'm not comfortable answering you". I like to reply, "Then I'm
not comfortable buying" or "When you are asking Mint price for an item,
you need to understand what the term actually means". Then there are
sellers who don't bother answering at all- really smart! In short, many
sellers forget that they need buyers a LOT more than the buyer "needs"
them. It's a basic concept that has sadly been lost to many on that venue.
Trent King