If you signed the NDA and after that they start selling/marketing your product, then they must prove they had everything planned before you sent/showed them the product. But all of this is if you sue them, otherwise nothing happens.
What I think you should do is research as much as you can about the company, if they’ve had any complaints, what kind of complaints do they have, is there any suggestion they might be unethical, are the complaints legit or just people trying to take them down. But generally speaking, big companies are fine.