Just to share what I know, usually authorised dealer is only willing to take in car less than 5 years old AND less than 100,000km on the mileage. And their offer price is usually significantly lower than outside, they want margin for maintaining their used car section mah.
If the car is older than 5 years old but with low mileage then they will probably act as a middle man to arrange disposal to a 3rd party car dealer. The disposal is usually under company's name (with or without marked-up is unknown).
I got my current ride from AB's regular 3rd party car dealer. Age=6 years old but mileage is geniune at 77,000km.
IMHO, if you sell privately or directly to the car dealer, you might fetch better price. The case in Singapore is slightly difference whereby they have this COE system/scrap value thing leading to a straight line depreciation rate. So their authorised dealers can go ahead and take in all trade-in car knowing the minimum "guarantee" paper value. In fierce competition time, many dealer offer "overtrade" value, which add a few thousand over the market value.
Just for reference and information only.