Oldfork

If you DIY, and I would, keep all the receipts for parts you used in the tune up. While you can't prove you inspected hoses, chain, etc., you can keep all records of parts you bought, oil, sparkplugs, bulbs, chain lube, etc. Dates of these parts would help as a record of when and how the bike was serviced. If I was looking at a bike, that kind of organization would tell me something about the bike and it's owner.