It is NOT typical to get your agency account flagged. Out of 100 ad accounts 2 get flagged. That's only 2%!
As the agency will review your page before allocating an ad account for you, making sure fb reps sees it, approves it or suggests changes if necessary, you will be 100% clean, therefore no policy violation should occur.
Also, agency accounts get less audits as they automatically belong to the GREEN compliancy level!
However if for any reason the ad account is flagged and appealing process is not successful, you may be charged $1,000 USD for each flagged ad account.
This is the agency's way to prevent any fraud or non-compliant practices.
Replacement account is provided upon request.