That's very weird. So you're saying that your retailer requires that you get it professionally installed, but the installation is already paid for, and you got a good deal. I don't see any advantage to anyone anywhere by requiring the professional installation. I'd wait for the guy to show up and tell him that you don't need anything done. Tip him if it feels right when he's there. I would suggest that you go ahead and call the installation guys before they bother to show up, but they might report your non-compliance back to your retailer, while the install guy probably won't.