Then why do some retailers manage it?
If you work for an independent then you are probably buying handfuls of cards at a time, so you are buying through distribution. I've also worked for smaller outfits like this and the pricing we used to get was about 5% cheaper than retail and in fact we had to buy from the "business" arm of "distributors" that also sold to end users, so you are buying from your competition. They have no reason to give you a big discount when they can sell to end users for double what they buy them from AIB's for.
OCUK are owned by caseking - one of the biggest PC retailers in Europe, they buy direct from AIB's. As do all of the other "big" retailers where they are buying pallet loads of cards.
If these big retailers are able to hit £700ish for a 3070 then obviously they are buying them below that, so that tells you how much your distributor is ripping you off.