Ya customer accounts is not something that can really be sold. Even with a contract, the contract has his name on it not yours. To get your name on it you need the customer to sign a new one which goes back to the original problem. They don't know or trust you.
When someone is selling a business they can sell equipment, trailer, truck. Then as a side bonus they can take you to each of the customers and introduce you but that's all they can do beyond that is a relationship that needs built between you and the client. If I sold out I would sell my trailer and equipment for $xxxxx.xx then introduce for no cost I can not sell people