Unless you've got something actually
worth buying as a part ex (eg: one bloke a number of years ago took his mint Mk 1 Ashtray GTE back to the dealer he originally bought it from as a part ex on a brand new Astra, the dealer then used the vehicle as a display/advert, rather than just flogging it on) then generally they're going to just throw your old car in the auction, and it makes what it makes. If it breaks even, then happy days (and even happier IF it makes a profit) on the other hand, if they give £500, and it auctions for £400, well, that great deal you had of £1000 off your brand new car, plus your old as part ex means they really 'lost' £1100 on that car/took off £1100 off it, for them. I offered to take a grlfriend's car off her hands, rather than the 'paltry' £400 she got offered as part-ex. What did I eventually sell it for? £415 after a
lot of stress. So not always are their part-ex offers unfair.
So I'm not going to rant about how evil dealers are etc.. theyve got to sell things for more than they buy them for, that's how it works, of course. The token amount of money they offer for a part ex is whatever they can spare, effectively, but like I say, generally the car will just get wheeled into the auction, and whatever it makes, it makes. And as said, the only exceptions are when it's actually worth keeping, tarting up and selling again.