Would this be mitigated by setting up custom demos with quickly mocked features on separate branches that can be easily spun up and deleted? I’ve helped clients with similar needs, and it’s so much easier to make a rough working feature branch for something that helps the sales process for a large customer, temporarily run it on a subdomain for demo purposes, and then get rid of it. It still hangs around for a time in a branch, but it only gets merged in when there’s a definitive need for it to be part of the live product.

Edit: This doesn’t solve the problem of wasted team effort, obviously. This kind of effort ought to only be taken when you can’t get a potential customer to agree to signing a contract before doing some work on a new feature. But that can be difficult to do sometimes. Marrying sales and development is its own challenge.