This is a very important tip. It's typically very easy to find former PhD students and postdocs that have worked with a given PI. Sometimes they are even liste

This is a very important tip. It's typically very easy to find former PhD students and postdocs that have worked with a given PI. Sometimes they are even listed in the PI's website, but if they aren't, they can be found by looking for the PI's papers and checking the coauthors, or in the case of PhD students by looking for PhD theses. Find their email address and politely contact them, asking about their experience with that PI. Most people should be happy to respond, and that kind of information is invaluable.