Turn this around, and see it from the "big wig"'s angle. They get in some guys (you) who obviously have not been around the block a few times already. More importantly, there is no attorney present and no way after the meeting to establish who said what, when, to who, in what setting.
His upside to screw you nine ways to Sunday is a big bonus. Where's his downside? Simple: none.
You cannot even name and shame as someone else suggested. Retain an attorney to properly advise you before you put names up here post-May.
Chances are the "big wigs" you met were not C-level, nor the level of management below that. If my guess there is correct, then you were not really dealing with "big wigs"; you likely were dealing with essentially middle management. The closer to middle management you get, the more prevalent this cutthroat behavior comes out. I could post a wall of text on why I personally have found this to be the case in my anecdata experience, but this response is getting long in the tooth already. At Fortune 50 levels, if you are meeting with C-level or direct reports to C-levels, there might be some mitigating factors that makes them more trustworthy, but again, I don't have the time to get into that here.
Suffice to say, when these impressive-sounding Names start dropping by, you need someone with the sales experience to qualify the opportunity. There are ways to generally suss out how serious they are about vetting your team/tech/org, mostly in the vein of making them come to you. Most middle management won't have the budgetary clout to spend anywhere close to what a Big Name will really spend (easily 5 figures and up, or an equivalent amount of staff time and expenses) doing just due diligence evaluation.