I worked there. It's a legitimate research firm. They do not sell things and most of their studies are scientific, though they do some market research to pay the bills.
If they call your cell phone, say it's a cell and they'll take the number off the list.
If you just want out of the random selection pool, say to block your number. They will verify the number and then block it.
If the person is rude, ask to speak to a supervisor. They want their interviewers to be as polite and professional as possible.
If you cuss at them or refuse to verify your number, it won't get taken off. They have instructions to hang up if the respondent gets rude.
Just be nice, most of them are exactly like me. Students at MSU that can't find a job in the small town. There aren't many jobs available, and this was actually a really good company to work for. They aren't bad people and what they do is respectable. Don't assume everyone is selling something.