1) Slop. Their guesstimates are *wide*, even within a given condition.
2) Vehicle condition (kbb.com does have a neat little tool to determine what condition they consider your vehicle to be in)
3) In my opinion, Private Party Sales are always a touch overinflated, and Trade-In Sales are always a touch under-inflated. Makes you feel good on either end (mostly because it seems that individual buyers look at Private Sales before buying, and people who trade in their **** seem to always look at Trade-In Sales before heading for the dealer. Desired result? Everyone likes their actual results when compared to KBB numbers.)
Well, you see the numbers from KBB....and I was 100% honest in my appraisal. It is probably less now, as I just put 1000 more miles on it to see my grand-babies.
I know the trade in they offer is always way way less than KBB mentions in any form. I laugh & walk out of the showroom. The only reason I didn't haggle more for trade when I got my Ram is I HATED the silverado I was trading in, and it only had 33K. It had problems that the dealer refused to fix for which there were TSBs, and it had problems they refused to even look at, and it was a CPO vehicle, which meant it was covered bumper to bumper until 48k.
The locking rear end stopped working correctly, and they claimed it was only designed to work when moving forward, not when moving in reverse. They never even opened the diff cover to look at it, even tho I could prove it was designed to work both directions. And the rear doors, they would fill with water when it rained hard, cuz the idiots put weatherstripping over the drain holes at the bottom, just to name a few.......