Yes, someone will find a way to buy cheaper on the internet, but there is a way around that.

I used to work in the printing trade, and sometimes people want to supply their own paper to print on. Paper has to be the right size for printing multiple images on, correct grain and suitable finish. Most printers will only accept customer's paper if it meets the printer's requirements, then if it is acceptable, we would add mark-up on the paper the same as if we bought it ourselves.

This is something that Installers can do, 1. Insist on approving any supplied equipment to ensure that it meets specifications. 2. Charge an inspection fee to cover the time involved. 3. Add a mark-up identical to the mark-up that you would add if you supplied the equipment.

This way it would discourage clients from purchasing their own equipment and it would insure that you would not be out of pocket if they did.