Hi All,
We run 3 loan cars, no charge, but built into each job. All are old cars, but well maintained, usually ex customers cars, so all up together for very little money to buy.
Disclaimer in car saying the person who loaned the car is responsible for all costs including fully comp insurance which the customer has to supply.

We have got insurance for loan cars, but don't tell customer, cost £500 extra on motor trades policy.

Being in the middle of no-where, it costs more in time running customers to & fro, than if they drive home in a loan car.

Very little petrol in any of them, they have to put some in (Garage less than a mile away)

Works well for us.

Regards
Steve