I as a dealer have always offered to take in part exchanges, sometimes even swapping one of my cars for someone else's (if in my favour). Now i consider myself a profesional in the field that i am in ie: car dealer, so when i get offered a vehicle as a p,x or swap 1st thing i do is do a hpi check, ALWAYS ALWAYS check out a cars history 1st, if you dont you could loose everything !
This comes from experience, my younger brother had a Mitsubishi Evo 6, value: about £8,000, put it on e-bay px / swap and was offered a BMW 530 M sport diesel on a 54 plate, the owner of the BMW said give me your Evo and £2,000, of course my brother jumped at the chance to own such a car, now this BMW has to be worth at least £18,000, i am the owner of a large company and fancy a change, i know my car is worth more than yours but i can afford to loose the cash, im loaded (that was what the owner told him !) After a few days of exchanging e-mails and phone calls the guy became very pushy and said we must get the deal done this weekend.
It wasn't till the day before he was supposed to go to swap the car that i said "you have checked it out havn't you " ? my brothers reply was, "he sounds genuine" i got the registration number and done a hpi check and guess what ? the BMW had over £20,000 worth of finance still owing on it !
Needless to say, the Evo still sits on my brothers driveway,if he had done the deal he would have lost everything.
If you take in a car that still has an interest from a finance company ( still has finance owing on it) the car still belongs to the finance company, and beleive me they will take it off you, which leaves you with nothing ! Dont sit there thinking "they wont take it off me !" THEY WILL..
So always do a HPI check..