Amazon is much more expensive and even more buyer-centric. Groupon isn't particularly busy and definitely aren't good with sellers. I've heard a lot of horror

Amazon is much more expensive and even more buyer-centric. Groupon isn't particularly busy and definitely aren't good with sellers. I've heard a lot of horror stories. Overstock is probably the worst, and I'd say downright abusive to their sellers. They also have no API or FTP. Rakuten, nee buy.com is a strange beast. They will pause your account for strange reasons. No API either. Walmart has little useful online presence for 3rd party sellers and no API. Newegg also has no API. I haven't heard any real bad things about them otherwise. There are a lot of niche marketplaces that do very well in their domain. They aren't using APIs. Some are absurdly expensive and others are cheaper. It doesn't really matter. No online market takes care of the seller, and honestly, the buyer is far more common than a seller. One seller leaves and another takes their place.