So what exactly is he doing if not importing it?

(Maybe you would have a point in case of AliExpress or Amazon and their European warehouses, but not direct from China.)
I don't think it's feasible to put this on trade platforms. It's not their product, they have no control over it whatsoever. All they could do is demand paperwork from sellers of certain items in certain categories. Of course, the paperwork will be fake, and good luck going legally after someone outside EU jurisdiction for violating EU regulations. If you ban their account, they will set up a new shell company and sign up for a new one. Good luck having auction sites play detective in faraway countries to figure it out. And who will pay for testing these products to find out that the seller needs banning in the first place?
Besides, as long as greed rules the world, trade sites have no motivation whatsoever to spend money and effort on reducing their sales volume. They quietly permit a lot of unethical shit already, and they will continue.
Education and Darwin are about the only effective solutions. Don't buy dangerous shit from places with zero ethics, simple as that.
(In related news, damn it, reading such posts reminds he of how fucking relieved I am that Brexit went through

)