Maybe some honesty would work. 'If you supply the hardware, I must charge more for installation. The sales profit is part of my business plan.' Then explain your overhead in great detail.
Or, make it a rule - must buy Crestron from you.
Or, sell all hardware at cost, and charge more for design, install, and programming for everyone. I think most clients would actually like this.
Just throwing some ideas out.
TB A+ Partner Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense. -Buddha