> ... the other is people ordering the real thing, repackaging it with fake from aliexpress and returning for full refund.

Can't you do this to a retailer?

> More enterprising folks sign up as Amazon supplier, register for some expensive products, ship real thing once or twice and then start throwing more and more fakes into their shipments, all nicely co-mingled by Amazon

Seems like a fast track to getting your account suspended. Why compromise a profitable business to basically skim off the top?