Pretty sure restaurants and car mechanics aren't unique skills and when they retire in my area someone usually buys them out and continues operating under the same name...
Going from my memory, "E-myth" book(s) insist on thoroughly documenting operating procedures and turning them into playbook. Rigid in terms of personnel training, but open to change if someone figures out an improvement. The goal is to be able to scale up operations into multiple venues (franchise models) while maintaining highly consistent appearance and level of quality.
As much as having such documentation will make it easier for a franchisee to get the business running (the books call it "turn-key business", IIRC), it will also make it easier for a potential buyer to take over and immediately hit the ground running.
But those will be different businesses. The restaurant will not make the same dishes or retain the same customers. The mechanic will operate on different types of vehicles.