"Do you also tell them that they will have to make numerous trips to the supply house for all the stuff they will need that HD doesn't carry?"
Ha ha, that's a good one. Actually we have a descent selection of material but of course I end up sending someone to a supply house everyday. I'm trying to get more contractor brands on the shelf (3m, Arlington, Slater, etc) but no luck just yet. Also trying to keep the popular items on the shelf is sometimes a hassle but it's getting too late to write about that.
As far as the markup goes, I think just about everyone is happy paying HD prices, the problem is getting in and out of the store as opposed to going to a supply house, no?