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Since you are collecting from the customer you are, in actuality, the primary contractor and the person you select to do the work is your subcontractor. You are the party responsible to collect the sales tax, file the returns and remit the tax to PA.
Sales tax is imposed on all repairs other than those performed for tax exempt entities. Thus, you are the responsible party for those taxes. If you go to the following link you will see the guide for construction contractors. You are in that group.
At the following link in section 10 you will find the applicable rules for construction contracts. Your agreement with the homeowner is a construction contract.