Not wrong to ask, but you should expect the contractor applied a mark-up unless your contract and scope of work specifically says otherwise. I suppose you should also expect the contractor to be transparent and forthcoming in their dealings with the customer.
Is 10% normal? For the contractor maybe, but some contractors may mark items up 20% or 30%. They are essentially re-selling a product and its up to the consumer to know if the price on that product is competitive or choose to purchase it themselves from a more competitive source.
This is why it is important when evaluating contractors for your project we strongly recommend requiring them to provide separate and specific line item pricingforlabor items suchas demolition, plumbing, framing, flooring installation, painting, etc. and finish materialquotes for things like flooring, tile, plumbing fixtures, lighting, doors, etc.
This approach helps both you and the contractor ensure thereis an accurate, aggressive and sustainable quotation for his/her services.
It also gives you the assurance that you can choose thefinish materials you prefer at the best possible prices and without having to pay any contractor mark-up.