Why are cars with nearly identical options/miles, etc. Valued with drastically different values? Are cars at dealerships valued higher than those being sold by private parties?

I have a car for sale, at the current price it's a "fair" deal only $685 below
market value.  However a dealership in town has a nearly identical vehicle
(same year, trim level, engine, color) and the dealer car has 2,000 MORE miles
than mine.  Yet the dealer car is a "good" value at $2,000 below market
despite the fact that it has more miles than mine and is priced $1,000 higher
than mine.  What the heck is going on!?