Given the interest in my "LinkedIn Spammer" post, perhaps there's a blog niche in describing what actions will get you banned from legitimate websites? Well, on Open Table, four no-shows within 12 months will get your account terminated.
However, as i recently experienced, if you eloquently explain the circumstances leading up to your missed reservation, they'll strike it from your record. Maybe there's a compassionate human being at OpenTable who just reads excuses and deems them worthy or not. Or of course it could be a "delete_noshow" script attached to the web form that automatically grants absolution.