Apart from the team scrutinizing and the whitepaper as you mentioned, availability of a minimum viable product as well as business solution is something you really want to be checking out first.

In fact, personally, whitepaper is usually the last thing i check. Basically, I visit the website, look at the team, check their LinkedIn profile page as I believe in this jet age, there is actually no excuse for a well-informed team and experienced one not to have a LinkedIn profile page over the years, and with this I check their past experience, dig further on them if they are for real, contact some of them if I could, ask questions on their ANN and social media pages, and then from there I look if there is an MVP.

As long as the team is serious and ready for business, there should always be a MVP before I even start considering going through the whitepaper for business solutions.