A: The short answer: Do Not Buy A Used Crib.
The rules for how cribs must be made take effect on June 28, 2011 and essentially make most cribs sold before that date obsolete and, technically, unsafe. After hundreds of incidents, millions of cribs recalled and an estimated three dozen deaths, the government stepped in and said that cribs were not being made to a standard that parents could count on.
Drop-side cribs, which had been the most common type, were determined to be particularly dangerous. They can no longer be sold in the U.S. You will see them at yard sales, though, but they are no more legal there than at a furniture store. Also, crib hardware and how cribs are assembled have been big problems - problems that are more pronounced with used cribs.