The value of a car is what the buyer and seller agree on. It’ll be higher for a mint, survivor 1969 Mustang, and it’ll be lower for a 5 year old Hummer H1.
It sounds like you have an appliance vehicle, which is good and bad. It makes the valuation more accurate (as they sell LOTS and LOTS of them), but your car may depreciate faster (because there are LOTS and LOTS of them).
You can make more money in a private sale, but you also have to include the hassle of advertising it, dealing with tire kickers, and the like. In a dealership situation, you have to deal with the underhanded crap the sales guy is going to run past you.
For our 98 Corvette, bought used in 1998, for $42,000 they tried to do the following:
give us lease rates based on the car being worth $45,000 and $50,000(!)
Charge us $350 for ‘window VIN etching’
Give us $7,000 for a trade-in that was worth $11,000
As it is, we ended up paying MSRP for a new car…for an 8 month old Vette with 8,000 miles on it…because it was in demand.
By the same token, I bought, brand new, a 2001 PT Cruiser for $21,000…I waited 7 months, bought it from CARMAX in Ga, had it courtesy delivered to Denver because they’d charge me MSRP and all the dealerships in Denver were asking $4k (or more) over sticker for them. Six years later, that car, with 48,000 miles on the odometer, was worth $4500.
TL;DR version: Buyin cars sucks, you will almost always get screwed, or deal with a lotta hassle. Your car is also worth less than you’d like…always. If not, you just don’t know you’re getting screwed.