If you only fail once in a while, that's not a problem. Some of the audits are really hard to identify as such (or correctly pass, for that matter), because they're based off individual decisions, not necessarily agreed-upon policy.
If you fail too many – and nobody really knows that number – you will be temporarily banned from reviewing only. No other restrictions will be in place, so it's not comparable to a full account suspension.
The algorithm is as follows: Given a 30 day window, the first ban will get you 2 days. The second one 7 days, and the third one 30 days.
Note that automatic bans are only in place on the trilogy sites (Stack Overflow, Server Fault, Super User). Moderators can still always manually ban users if the system didn't catch them.
