Mate, if he is loosing money on each job even though he is not buying the right amount of adhesive then he seriously needs to alter his prices. Don't make his problem your problem, porcs is more than ceramics all day long. Don't alter your price cos all that will do is annoy you while your working and the only one who will benefit from you going in cheaper is him and the end user.......... And who do you think will get the blame if a slight problem occurs. Don't come down on your price. Tell him to come down on his plumbing price and up the tiling price, i bet he wouldn't even consider that!! so treat yourself as he is treating himself cos at the end of the day your the tiler and it's your business and you state your price.