we will in certain situations...

1)some of our commercial customers get better prices for things like lamps and ballasts from their corporate buying program than we get. So we install their part, and bill them our time.

2)smaller commercial/residential that are on "flat rate" jobs, we simply will back out the cost of the material (leave in the markup though) and remove any warranty for the product. If there is a defective product, they pay extra for us to replace it, etc.

3) but if we were doing these smaller jobs at T&M and relying on the material markup, i'd probably talk them out of it.