That is absolutely common and is part of cost and performance accounting, which is probably also taught in vocational school for craftsmen. A standard method would be, for example, at least to add the overhead costs to the purchase price of the materials. Usually, though, they also want to make a bit of profit, yes. The difference could be that a hardware store makes a 10-40% margin on the materials (probably very different depending on the product category), while a craftsman makes possibly 30-50%. Depending on how they calculate internally.