Question about certain staffing agencies.

I've been applying to several positions in the biotech field, and I've been getting calls from Indian recruiters. We have a brief discussion about the position, they make me confirm to a RTR (right to represent), then I never hear from them again. I'm not trying to be prejudiced, but are these staffing agencies scams? They do give me legitimate job descriptions, they're offering me positions with real companies, and they're not emailing me through gmail accounts.

The staffing agencies I've had conversations with are MWIDM, Net2Source, Compunnel, and Mindlance.

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