I have very recent experience of selling a car to a main dealer and it was very positive. It wasn’t a part exchange either, as I had already agreed a price without part exchange a few months before. I bought one of my daughters a Hyundai i20 in early 2016. I drive a hard bargain and got 20% discount, so the car only cost me £12,600 new. I ordered her a new one in September. Discounts are harder to come by now so I only got 11% off this time ? .
My intention was to sell her old car privately. When her new car arrived in December, a few days before we picked it up I called the dealer and asked how much they would give me for her nearly 7 year old i20, more out of interest than anything (in the same way that I always ask Motability what they want for our car at the end of a lease, before laughing and handing it back). Anyway, they offered £8,400, so a total of £4,200 depreciation in almost 7 years on a car bought brand new. Needless to say I bit their hand off and it saved me the hassle of selling it privately.