Exit terms are usually negotiated at the worst possible moment, which is when one party has decided to leave. Positions harden, the conversation becomes about fault, and whatever gets agreed is shaped by leverage rather than by what is reasonable.
Every proposal here states the exit path alongside the scope, the fee and the limitations. What notice is required, what is handed over, what the client keeps, and what the firm stops doing on what date.
What it does to the sale
It removes a thing buyers worry about and rarely raise. The concern with any embedded or retained arrangement is that leaving will be difficult, and a buyer who has that concern and does not voice it simply does not proceed. Answering it before it is asked converts a silent objection into a stated term.
It also disciplines the firm. An engagement that has to be leavable cannot be held together by dependency. If the client can take the system and run it, the retainer has to be worth buying on what it does rather than on what it would cost to unpick.
Handover as a deliverable
What was built, why, and how to run it is written down during the engagement rather than assembled on the way out. A system only we can operate is a dependency we have sold you, and it is worth less to you than the version you could run yourself, whatever it costs.
The uncomfortable implication is accepted. Some clients will use the handover and leave, and they will be right to.