Can I trust a new Market Research Firm?

I would not without thoroughly investigating and verifying their legitimacy and success.

That is certainly a loaded question. Do you have reason to doubt their authenticity ? Have you heard something about them that makes you doubt it ?

How do you trust a old one ?

What sort of research ? What is results to be used for ?
Who is paying them,
Who are the principle people, and what are their histoies