Reply by Jorge G.

For wood I mark up the amount of “waste” my design indicates. There is always waste on boards and sheet materials, this way I know I am covered if I make a mistake.

For hardware, slides, handles, etc. I only mark up the delivery charge as I don’t want to nickel and dime my customers for what a amounts a pittance.

-- Just because you’ve always done it that way doesn’t mean it’s not incredibly stupid.