I have a very simple bookmark let that only shows items sold by Amazon.com without having to filter by category. I think part of the issue is that their site UI is pretty horrendous, and makes it difficult to limit searches. I do however notice issues with some items sold by them, but primarily with descriptions being incorrect or them combining a bunch of items with reviews, sometimes for completely unrelated products. I personally try to avoid third-party sellers for the most part. I would love to support smaller businesses, but to be honest you're probably doing most third-party sellers a disservice by buying on Amazon, especially if you think there is a possibility that you'll return the item.
More than that, you have to trust every seller for the product you're buying, because all inventory from all sellers (including Amazon itself) goes into a single bin. You have no way of knowing which seller actually put the item you get into the bin.
