For listed businesses, I verify that they are still on the exchange by searching their stock symbol on one of the many stock sites on the net and print out the nifty little quote that pops up. I review the banks that we deal with to make sure they haven't been merged or sold. For the government entities, such as local government, I generally don't do anything, but someone suggested putting a copy of our property taxes in the file to document that they still exist!
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Knowledge is knowing what to say. Wisdom is knowing when to say it.