Are you thinking of collecting (pre-paid?) orders from EU citizens (correct term?) and then importing in bulk, breaking down the bulk to fulfill pre-existing orders?
So your customers are buying the products while those products are still in the United States? And then you’re shipping them in bulk to the UK and distributing them to the customers who have already bought them?
It seems like an unwieldy plan. How are you going to be sure you have enough customers to fill a bulk order? Are you going to tell the customers they can place their order now but have to wait until twenty other people have also placed orders, even if that might take a few weeks?
On a separate issue, what’s the advantage to the customers of getting you involved in the process? Why don’t they just order directly from the American seller and have their product delivered to them directly?
That’s an interesting model.
Here’s my totally uneducated guess - the question is, who is doing the selling, taking payment, etc.? If you as EU company are the recipient of the money, the EU might consider it an EU sale. If a US-based corporation on a US-based website, takes the money, then the sale happened in the USA. Presumably, then the US company pays your company to be a secondary shipper. (“We ship you a pallet, you break it down and forward it to the supplied addresses”)
Your problem will be of the variety “you can’t fight city hall.” If the EU customs people suspect that there is something that approaches “re-selling”, then they might always (I presume) hold your shipment for the 6 to 24 months or more it takes to make a decision. The wrong decision - they could decide to seize and dispose of the shipment. Unless you can afford expensive lawyers, perhaps you will be stymied and some expensive product tied up. There may be legal precedent about at what point breaking up a palette to reship becomes reselling. It may depend on how much you and the US seller are at arms-length or if the companies are intertwined. If your EU company has a finger in both the order process and the shipping… How involved is your EU company in any advertising?
All these “maybe’s” boil down to “ask a lawyer knowledgeable in the field of EU imports before risking a large sum of cash.”