One of the biggest issues I have seen with home A/V installations is that the labor rate is way to low, and way under budget... so they make up for it by overcharging on products.
Now, with my side work, I try to compete with internet pricing or stay within about 10% of that pricing. One thing I tend not to allow is CFE (Client Furnished Equipment) for cabling. I don't gouge on pricing for anything, cabling included, but I do custom make everything (except HDMI) for the client so it fits nicely and is the right length, the first time.
CFE gear is nifty, I write it into the contract and include verbage to discuss it. I'm 100% not responsible for CFE. It must be on site, ready to install when I get there. It includes a full charge as if I had sold it to them, and then carries absolutely zero warranty, setup, or guarantee from me other than the most basic of setups. It is inappropriate to expect me to know every piece of gear on the market or to spend 2 or more hours researching your product that I will never touch after selling it to you... if you aren't going to pay me to do that.
But, if the client understands this, then I have less of an issue with them purchasing the gear on their own than most places. I do have problems when a client doesn't want to discuss pricing with me at all as there are times I can adjust my pricing just a bit if it makes it competitive.
When the day comes that a client has a projector malfunction, that I installed, but did not sell them - and that client expects me to diagnose the issue at no charge... Well, then I likely will feel differently.
When's the last time you brought your car in for service and told the mechanic: "Hey, brought my own brake pads, rotors, oil, and filters... just need you to install it all!" I think that CE installers need to get their focus on labor numbers to ensure that everything is accurate. If a job is going to take 12 hours of installation, 4 hours of design, 4 hours to program, another 5 hours of travel time, etc. then those numbers need to be figured into pricing from the beginning. Then as parts are bought, or not, by the client, nothing else in the price changes.