I’ve read this past week on that other Motability site to get the best price for the car is to ask the dealer who you would be returning the car to to buy the car from Motability then sell it back to you.
The dealer gets first refusal on the car if you don’t buy it first and I’m sure they would get a couple of thousand off the price that Motability offer you for said reasons noted above.
The dealer will want a cut for sure and I don’t know if this actually works but in theory it should.
If you do buy the car direct make sure everything on the car in the way of consumables are all up together with the likes of tyres and the likes and get these renewed a few months before asking for a price to buy because once they give you a price it will be on a “sold as seen” basis so no come back if you noticed a couple of tyres are near to being worn out or the wiper blades are smearing the screen and need renewing a few days after agree to buy, they will ring you and ask if your happy with the car the way it is along with any scraches in the paintwork or dents.