Also, Amazon purposely mixes catalogues and advertises their own stock together with third party goods, and there's no clear wall on the site between them. If you look hard enough, you can see which ones are third party, but for a casual buyer it's all the same space. It's like if I came to Walmart and random goods on the shelves were "third party" and Walmart tried to claim they have nothing to do with it, just renting out the shelf space. Probably wouldn't fly very well in court.
I don't know if they still do it, but for the same SKUs, there were stories on HN about how they mingled the stock.
So you might get blamed for counterfeit goods sold by someone else if Amazon fulfilled an order with the 'same' goods provided by another seller instead of those actually provided by you.
I haven't heard that leading to any lawsuits like this, but it easily could be an issue in the future.
Amazon:
A) takes the payment (and later disburses it net30/60/90 whatever) instead routing of it (possibly less a fee) directly to the seller
B) Doesn't allow communication directly between the seller and buyer
C) Requires already fairly significant restrictions on the seller
I don't think eBay does any of those things or at least not to nearly the same degree.