They can't sell you everything(at a below list I believe on that sight) and then spend 30-45 minutes mounting and tuning it for free.
Why not? It's part of doing bussisness and building a clinentel. If the shop doesn't think so I"ll elect to spend my money elsewhere. Sell it at suggested retail and install the accessory at no charge. Personaly I don't have that problem, I can work on my own bow.