How do you tell when a big customer is pulling your business in the wrong direction?

“Listen to your customers” gets complicated when one customer is worth enough money that their requests start carrying more weight than everyone else’s. A request comes in that’s slightly outside what you normally do. It seems reasonable, and keeping the account happy matters, so you agree. Then there’s another exception. Eventually, your team is running a separate process for that customer, but everyone still talks about them as one of your best accounts because of the revenue. I think the difficult part is that this can also be how a business discovers a better offer. A customer asks for something you hadn’t considered, you figure it out, and other customers end up wanting it too. Refusing everything outside the original scope would close off some useful opportunities. The test I keep coming back to is whether you’d want ten more customers just like them. That forces you to consider what happens after the sale. The contract might look great while the people doing the work are spending half their week handling exceptions. Or the account might be difficult because you’re learning something that will make the next ten easier. Those situations deserve different decisions, and revenue alone won’t tell you which one you’re in. Before calling an account a success, I’d want to hear from whoever actually has to deliver on it. Especially whether the extra work is becoming something repeatable or still depends on someone dropping everything whenever that customer calls. For people who’ve been through this, what helped you recognize the difference between a demanding customer worth building around and one you needed to stop accommodating?