if someone says they have a billion users because they are connected to the doubleclick exchange... they aren't lying, they might be deceptive or simply foolish.

As part of due diligence, the buyer/investor should ask how these numbers are calculated and make their own judgement. Unfortunately I believe startups select for those who dance the border of deceptive and foolish.

> they aren't lying, they might be deceptive

I think that’s well within the bounds of what most people would consider to be a “lie”. The legal system has more specific definitions, though.