If the homeowner is getting multiple quotes, you may have a hard time getting the job if you are marking up a subcontractors estimate. The fact that the homeowner has asked for a quote from your landscaper friend kind of kills that deal. Your friend will have to do what is in the best interest of his company. However, it is a pretty sweet deal if he will pay you $15 an hour while he teaches you how to compete with him. You will not have to worry about losing money on the job, carrying the expenses, and/or messing up the homeowners drainage all because you dont have any experience.