Personally I'm fine with someone with good mechanical knowledge doing the very simple things and documenting them. For all scheduled servicing and more complicated jobs I want to see stamps in the book and documentation from a professional Ferrari mechanic or a dealer. If I enquired on a car that's going to cost a couple of hundred k at least and discovered Old Mate did all the work in his back shed that's where my enquiry would end. It's not just the lack of stamps in the book, it's the impression of cheap-skating that would put me off. That may be unfair and obviously others feel differently, but it's my money.