Isn't this the normal sales anyhow for many products? One attracts a customer with unreasonable promises and features, makes him sign a deal to integrate, then issues appear once in production that make you realize you will need to invest more.

When you start something (startup, FOSS project, damn even marriage) you might start with the best intentions and then you can learn/change/loose interest. I find it unreasonable to "demand" clarity "at the start" because there is no such thing.

Turning it around, any company that adopts a FOSS project should be honest and pay for something if it does not accept the idea that at some point the project will change course (which obviously, does not guarantee much, because even if you pay for something they can decide to shut it down).