Due diligence is a valuable skill set
Some professionals do this as a big part of their job. They're skilled at researching and digging. They look for the problems, the flaws and threats.
Most candidates for jobs don't know how to carefully evaluate a new opportunity. If they do any kind of due diligence it's surface level skimming at best. Then, they wonder later how they landed in such a mess.. Worse, they see the red flags but choose to ignore them because they don't want them to be true.
There are numerous sources to use in evaluating the objective aspects of a company. Financial reports, news stories, government filings, industry resources are just a few. LinkedIn can be a good tool to investigate the people who work there. How long have they been with the company? What did they do before? Don't forget about the people who list it as a previous employer.
More importantly, candidates have little idea on how to evaluate the subjective details of a company. What is the culture like? Do the people look happy and work well together? Do they respect their leadership?
Decide what's important to you going into the interview. What do you want to know? Then, figure out how you will get your answers.