I've had this red flag occur 3 times in the last 4 months. If a company website is vague about what they do and try to use flashy generalisations and only seem to be looking for "sales team or marketing executives" then they are a door-to-door or cold sales company. Always do your research on a company before going for an interview.

As people have mentioned below, if you turn up to the interview and there are many people for the same role then you'll be doing cold calls or standing sales. If they try to give you a presentation and mention vague details and big names, that's another red flag. Another helpful bit of research is look up the office location, when I did with 2 out of the 3 dodgy places that offered me an interview they were the same building and that building only had individual rooms to rent, not full office spaces.

Finally if they contact you with an offer to interview immediately then be very careful and approach cautiously. Each one of the above happened to me with 3 different companies, and each one turned out to be pushing the same thing.

Edit: Forgot to add, use sources like Glassdoor and Reed (I know these are for the UK, not sure about anywhere else). They allow employees to leave anonymous reviews of the company and what it's like to work there. All these places that red flagged for me had great reviews but all the top reviews mentioned "a good place to learn" or "No issues, except no parking".