Maybe Mav can help me out on this (again, LOL).
All you guys need to do (assuming this is a legitimate question).. is to simply ask the Firm for their affiliations (Which exchange, their Clearing Firm (be sure they're not a "sub-llc" of some other firm of course)... then ask for a copy of (yep, you guessed it Mav) their balance sheets to see not only about their capitalization, but their audited condition overall ...as in connections with others etc.
The primary firms are all happy to share this info... and, as I do, respect you for doing your due diligence.
All the best,
Don