Once was when 5 chargebacks came in on one day early in a month from a set of 5 credit card payments made by a single scammer; that put my account over some chargeback percentage level allowed by my merchant account provider and they terminated me on the spot after years of service. I had to ask dozens of customers with monthly subscriptions to sign up again with another payment provider, not all of them did.
The second time Google decided it would no longer allow AdWords ads for an entire category of (perfectly legal, non-scammy) services and suspended all ads in that category, including mine. Overnight my largest source of customers is gone and is never coming back. There's still Bing/Yahoo! but nobody quite matches the reach of Google for online advertising.
At this point I plan backups for the loss of every possible business relationship just to keep myself sane... while praying I never have to switch to the backups because there's obviously a reason they're the backup and not the primary.