ive had this before, trouble is some customers want it all, they want you to supply the materials, trade, yet want to keep or see the reiciepts, trouble is if you have told them your getting the materials trade, but keeping a little back for yourself, which in imo your totally right to do.....its called business ,.... there still getting it cheaper and your making a bit too, after all your sorting it out, picking it up, and will be the first one they turn to should there be a problem, as others have said there receipt is your invoice for supplying and fixing...