The first thing you have to do is ban USA-based online marketplace companies from hosting foreign vendors. Then you can better regulate what is left.
replies(2):
Of course can't hold foreign marketplaces responsible at all - but that is a different loophole we can close (if it becomes a problem Amazon will ensure it is)
Regular people are not someone custom wants to make an example of for ordering from a banned foreign company. Large companies will carefully check their supply chain to ensure they are not buying goods from banned companies, but tiny companies and regular people won't care as much.
I expect that the EU will have (if they don't already have) rules similar to the US and countries there will generally enforce them. However other countries (China!) will not care as much.