This advice seems to cover a corner case: If you might not be paid, don't put yourself under contractual obligation to complete the work. It opens up problems for both sides, though. I thought that proof of a signed contract would've been a given in this situation before any information would be shared and before the work would commence. It seems like a no-brainer.
The NDA itself? Well, if they aren't forcing you to sign that, I'm not so sure why you would.
The NDA itself? Well, if they aren't forcing you to sign that, I'm not so sure why you would.