The big problems being ...
As already mentioned, this cannot possibly work.
If the items carry a CE mark then the seller can "claim" that they are compliant and the big four are abusing their dominance by blocking legitimate products. Get the popcorn out.
But as already said, the CE mark is something the manufacturer (or importer) sticks on a product themselves - supposedly after having gone through the right processed to ensure compliance. So for "cheap tat" knockoffs shipped direct from China, there really isn't a way to know if the CE mark is genuine and the product is safe, or it's just the "Chinese Export" mark. Even large professional retailers in the EU can get caught out - there are plenty of tales of them having goods (eg USB PSUs) made in China where the samples are all OK and pass (eg) EMC testing, but once the production units start flowing, there are components (eg input filtering to achieve EMC compliance) left out to save manufacturing costs.
The average punter won't have a clue how to spot the genuine & safe "kettle lead" vs the dangerous one with unfused plug (OK, that should be obvious - but the rest not), non-conformant plug size, sleeved earth pin, undersize copper in the cable, etc. The average punter doesn't know the details of BS1363 - just that if it fits a "13A socket" then it's a "13A plug". Once you get into more complicated things (like laptop PSUs) then there's no chance.
I can see this being almost completely ineffective, while screwing up honest vendors caught up in "bad feedback" from dim witted buyers.