Yeah I've encountered at least a couple of recruiter companies who were really weird and gave me bad vibes and decided not to continue with them, trust your gut, what made me think twice about these recruiters:
1- Unusually bad English (Not talking about normal immigrant English like mine, but like really bad, no way someone hired this person to recruit for these kind of positions). 2- These `recruiters` talk in very low volume, I had to tell them to speak louder, my guess is that they are in an office with a lot of people doing the same. 3- They ask you about weird stuff in their e-mail communication, like sign something in early phases of interviewing. 4- When tell you when they will call you and the number is flagged as 'SCAM LIKELY' then they tell you to save the number, super red flag
After that I googled the companies / job postings and were super generic with bad reviews in glassdoor.