We have sold a lot of stuff to KEH over the years, many thousands of dollars. The buyer visits us, and he does a cursory evaluation and general operational check on each item - hey it will be THEIRS.
Most items we sell to them rate as excellent, and that is how I generally rate stuff we take in on trade.
Most items you have in your collection would rate EXC unless they are REALLLLLY NICE (or bad), and this is how we view most items we take in.
The differences between EXC+ and EXC can be very small, in fact, almost indistinguishable in my experience.
Any item rated as EXC or above should be operational, the meter may be off a smidge, since generally there is no easy way to check that in the field, for example.
Our experience and that of our customers is that KEH is pretty straight and generally fair in valuations. However, I don't think personally, a $30 offering for a Nikon N65 (Canon Rebel G) is 'fair', but that is where the market is these days.
Pretty hard to complain about the cost of even good 35mm gear these days. I remember, not long ago, when a Nikon N65 retailed for at least $100 new.......