We give clients options.

1. Buy them from us at our price and we handle the whole process
2. Give them a list of brands to shop wherever they wish. Warn them that improper selections, off brands that are not integrator friendly etc, will cost them time and money.
3. Offer a "concierge" fee to procure displays from a retailer of their choosing. (On smaller jobs I will charge them for my time to swing by Costco or something and grab a tv for them). This is just a selection and delivery fee, nothing more or less. Funny thing is it I usually make more doing this then the margin on displays.

If they choose #2 I make it clear to them that our responsibility consists of taking the display out of the box, attaching the mount, sticking it on the wall and connecting it to our equipment. TV DOA and it has to be shipped back to Amazon? Not our problem.

I have had more then 1 well heeled client show up with a half dozen tvs stuffed in their Mercedes SUV, interior now scuffed up from the boxes. He was such a cheapass about the whole process I even refused to dispose of the empty boxes for him. He seemed hellbent on making sure that we (and every other trade) made no money on building his house (that cost over $10,000,000).

Penny wise, dollar foolish.