You pay nothing up front.  All valuations, surveys and standard sale legal fees will be paid for by the provider.

All arranging firms like Rent Back Scotland will make money either by fees or by commission or through a combination of both.  Rent Back Scotland will receive a commission from the buyer and will probably charge a fee for this service, but this will be covered at completion, and any quotes will take this into account.  All fees are discussed on first contact.