You think intermediaries (e.g. dropshippers)
  can't add value to a supply chain?

These days, don't Chinese companies mostly list the products on Ebay and Amazon themselves? Just today I ordered something on Ebay and got a paypal receipt for my payment to 覃尚田.

I don't see what value an extra intermediary adds in that situation?

Dropshippers add range and access to market segments the manufacturer, or wholesellers, cannot ofer. These dropshippers are able to go after small customers with low order volumes. So they indirectly add value by increasing revenue.

they also cut out other middlemen like wholesellers and brick-and-mortar retailers. Done well, and at scale, this could be one of the more serious thrats for Amazon in the future.

> These days, don't Chinese companies mostly list the products on Ebay and Amazon themselves?

Yes, it's pretty standard to find the same company with store-fronts on AliExpress, Ebay and Amazon. It's sometimes worth checking for differences in prices though due to lag in updating each catalogue.

Faster shipping, added support, ease of returns. I am sure there are many other ways those "useless middlemen" could also add value.

Absolutely intermediaries in supply chains can add value.

can being the operative word. Amazon, New Egg, WalMart et al. opening themselves up to a certain sort of very low effort intermediaries sucks quality out of their platforms and makes online shopping a minefield of avoiding knockoffs (sometimes with Amazon impossible, to the extent where there are certain things you just shouldn't buy) and fake or paid-for reviews.

Fixing artificially low shipping won't kill this sort of behavior but it will make it easier and more profitable to compete against.

If they provide some level of stocking and quality control, they can. Dropshippers arbitrating between amazon and aliexpress don't really provide much of that.

What about insurance brokers? Or travel brokers? They don't have stock. Intermediaries (sort of) inherently create quality control via having a better perspective on the market than any single supplier can, and through pressuring individual suppliers via their own large-scale buying/selling activities.

E.g. if a dropshipper is selling mobile phone covers at scale, and stops using supplier x because the poor quality is affecting the dropshipper's brand, this puts more pressure on the supplier than if individual end-users stopped buying their products. Same applies to all brokers. They glean great power over suppliers in this fashion, while improving the experience for end-users (prime example: Amazon).

That isn't what happens though. Quality control with foreign suppliers is very difficult. A bad supplier with a bad name will disappear and come back with a new name. The shops are small and there are an enormous amount of them so there is very little what you might call reputation capital. Find people with experience sourcing products in China and get them to tell you stories.