I had this very thing with Ford.
First Motability car and identified the Kuga as perfect for our needs. Existing car was a Volvo S40 and didn’t want the hassle of selling privately so wanted to trade it in.
Fords in Kendall, Cumbria said exactly as previously mentioned. Wouldn’t give a trade in price but said they would put it through auction and what ever they got we would receive back. Didn’t accept this offer as it seemed very uncertain.
Phoned Ford garage in Liverpool where we have family and told over the phone the trade in price, deducted the AP from that and gave us a cheque back for the balance. Guess which garage got our business.