Part One: Strategy · Deciding what to build
A large customer asks for something only they need, and the money is real. Everyone else then lives with a product shaped around someone else's business.
A company makes ordering software for restaurants. Its largest customer, a hotel chain, wants every order approved by five levels of management, because their finance department says so. The renewal depends on it. Nobody should pretend this is an easy call. That contract pays salaries.
But a product is one thing, shared by everybody who uses it. A feature built around one company's org chart shows up in every customer's settings. Every later change has to avoid breaking it. And the customer's next request will arrive with the same weight behind it. After a few years the product is a record of old deals, and newcomers wade through options that exist for companies they have never heard of.
The big customer is not well served either. They get a one-off feature, maintained by people who do not understand their business, inside a product that is slowly growing away from them.
The salesperson with the deal and the founder with the payroll want the yes, and they have a point. So the request cannot just be waved off. There are honest ways to meet it. Look underneath: perhaps many customers need a second sign-off, and one extra approver is a real feature. Or meet the need outside the product, with an export, a connection to the customer's own system, or paid custom work that is called what it is. Or decline, and accept the risk. The one thing not to do is build it quietly and hide it behind a switch.
If the decision is not yours, do the looking underneath before the meeting. Bring the version others could share, and the price of the custom one.
Therefore:
When one customer asks for something only they need, look for the problem beneath it that others share, and build that. If there is none, meet the need outside the product or decline.
In practice. Before agreeing, name three other customers who would use the feature as requested. If you cannot, it is custom work. Price it and place it as custom work.
Goes with. This is SAY NO BY DEFAULT (23) with money on the table. What sales may offer is a matter of PROMISES YOU CAN KEEP (16). The switches left behind by old deals are candidates for TAKE THINGS AWAY (27).