What tilers used to do in my store was send the customers in with their measurements, we'd give them a quote on a couple of ranges they liked, let them take some samples away, the quote would be retail price.
Then the tiler would come in, order the ones they wanted at their trade price, and the customer would pay the retail price, or near to (tiler sometimes give a bit of a discount). So the tiler made some money on the tiles but the customer saved a bit too.
Thats exactly what I do Dan, If I get near the VAT threshold I wouldn't supply from that point onwards just let the customer take a %age of my discount