You can easily know if the engine was ignored when you remove the valve cover.
It isn't rare to see an older car that needs power steering repairs, but is in otherwise good shape. I frequently work with Nissan Maximas, and their engines and transmissions last for a long time, but when those cars are 12 years old, or older, sometimes they are worth so little, that the owner can't justify the expense of a new power steering rack and other suspension parts in need of replacement. A mechanic will often buy that car cheaply and drive it for many years, or quickly sell it for a nice profit.
If you really want to know if the engine was well-maintained or not, removing the valve cover usually helps. Having some varnish is okay, but beware of sludge or coke.