I've never looked into the ins and outs of it, but do B&Q not have trade counters at their bigger superstores ? We have two in our area, and I know at least one of them has a trade counter. Surely, this would imply that tradesmen other than yourselves, *are* prepared to use them as a supplier, and presumably, if they are going to offer such a service as a special counter for bona fide trade only, they must be offering some sort of discount over the shop floor retail price ? If that is the case, then the customer can pick what they want at the retail price, and you can get your markup on the parts, by buying at the B&Q trade rate.
Arfa