What happens to cars you part exchanged with Audi?

[Smithy]

Had a VW Passat before and got myself an Audi. It is quite old VW (2017) but I wander what happens to these vehicles which are not Audi's. Do they go to auctions or do they sell them to a dealership. Are there any example or prominent places audi would sell them at.

Edited February 18 by Smithy

[Steve Q]

They'll go to auction. 

[enc]

Some dealers would have had “contacts” who would take the cars not suitable to retail at the dealership. This doesn’t happen so much now instead,  none brand, too old or higher mileage cars tend to go to auction. 

[Magnet]

As I understand it, in these parts, non-retail stock cars are tendered to local dealers. If no interest is shown then the more costly ( and it can be costly) route of sending to auction is followed. 
Any particular reason for asking Smithy?