Fool me once shame on you

My sister asked me if I would help her to buy a beginner guitar for her son so she could give it to him for Christmas. She doesn’t have any credit or debit cards, or a paypal account to use to be able to order one online for herself. She has found the one that she wants, and she told me that she will get paid this Friday and give me the money to pay for it. I told her that when she gives me the money I’ll go ahead and order it and use my paypal account to pay for it. But I’m not going to order it before she pays me! I’ve been burnt before! Fool me once, shame on you, fool me twice shame on me!