All middle men are destined to be automated out by the system, if they add no value then sooner rather than later. However, people selling stuff online in niche markets are still somehow surviving, but sooner or later someone will figure out where they are hiding and get them too. It's all a matter of time.
When they add value, they thrive. When they stop adding value, that's when they get into problems.
Note that whether or not middlemen add value is not under their control. Local resellers add much less value than they used to now that global e-commerce works. Recording labels added value until the Internet came, and now they don't.
In this case small players can have advantages that big players don't. For example should I start shipping container loads of fidget spinners (latest thing among the youth here) from China to Finland I would have all kinds of things to take care of. User manuals, product safety issues, customs, local value added tax, consumer protection things etc. Small sellers operating from China can escape many of these.
I've recently got into 3D printing. I bought a printer from Amazon DE (directly from Amazon, shipped from Germany) that is known to cause fires (but can be fixed with a few simple mods). I doubt it would be allowed if it was made in Europe, but somehow Amazon have escaped regulation and sell these products cheaply made in China. I guess they pay taxes and customs so everyone is happy :-)
