Like LK, when quoting a job I don't provide a breakout, a change order is another story.
If any of us told our mechanic we would supply the crank shaft and bearings to fix the van because we can get a better price, he/she would tell us to have the parts store guy install them while we're there.
I don't know how a company can grow (or survive) simply being a labor broker, sales are as much a part of a profitable business as the labor.
I agree with A-Line's approach.
Roger