Well, let's look at it this way... You (dealer) go to a customer that needs a small, no frills system with 6 phones,quote the X-16 and the customer Googles it. They find that they can buy it at Sam's for less. What do you think they'r included to do? They'll either buy it at Sam's and either try to install it themselves (which they may be able to do!) or ask you to do the install for them?!
Either way, you lose!
You're looking at this way wrong. First, don't market the X-16 as the X-16. Call it Jim's Wonderphone 16 or such. The days of the customer caring about the name on the system has been gone for years. It' so easy to make brochures and labels that it isn't even an issue. Contact your equipment provider and see if they have any issues with this. Some don't
Secondly, what do you mean you lose when you install customer provided equipment? I had one heck of an argument with my business partner a couple of years ago concerning this point. If the customer provides the equipment we have utterly no liability. Everything is billable. We don't provide the warranty, free advance replacement, nothing. The customer pays full installation price and pays for any service or training afterwords. Frankly we're getting to the point where it is preferable to install all this stuff they buy from eBay and online vendors. The margins are very high (labor only) and no back side costs.
I've been in the business since 1971 and have seen a lot of changes. Embrace change and work it to your benefit. Any other course of action just causes stress and unhappiness.
--Bill.