I just bought an Accord recently and a quick glance at it’s CarFax shows that the oil was changed at regular intervals ONLY because the previous owner elected to maintain their car at the dealership. It even showed other stuff like brakes, tires, even when a new starter was installed.
But I STILL had the car inspected by not one, but 2 mechanics. My shade-tree friend and my regular Indy mechanic. So it’s important to have a car inspected, either way.
There are alot of things you can inspect yourself. Check this out, it will get you started.
A couple of illustrations down it shows Clean engine vs. Dirty engine based on an inspection of the oil filler neck. Anyone can do that. It also shows what the dipstick is supposed to look like.
Good luck hope this helps.