It has to be done while the fondant is soft, or it will crack. I use the diamond cutter, I find it is the easiest and best looking way for me. However, if you're using extra buttercream underneath, you'll probably be pushing harder...
Since you are not paying credit card or paypal fees, you could decide if you want to pass that savings on to him. Personally, I would, because there is no way to dispute anything when you pay cash.
Some people just have to have SOMETHING to complain about. Heck I see it ask the time on this website. I checked out a tutorial the other day and several people left rude comments. Someone took the time to share and be helpful, and...