I’d need to understand that he is a competent and qualified mechanic. Otherwise I’d view the seller as a skinflint/tight ass and I’d adjust my price offered thus wiping out the money he’d saved
If someone has been servicing their car regularly over the years and its still running, then that is a pretty good indicator they are competent. Qualified…you don’t need to be qualified to drain some oil out, replace a few filters, flush the coolant, change the brake pads. Just practically minded and have your head screwed on.
If you are looking at bangernomics, then obviously you will be looking at lower value cars with the majority of the depreciation already lost. I think you’ll find the costs saved from labour charges are equal to or several times less than the price you are paying 🙂