Back in 2011, the government changed safety standards for baby cribs in response to infant deaths related to old designs.
Though drop-side cribs used to be common, they are now banned. Plus, the new rules require stronger supports and hardware.
The problem with buying a used crib is the chance you might end up with one of the many that have been recalled. It may be easy to avoid drop-side cribs, but unless the seller can provide the original sale information, you may not know whether the crib you buy meets the latest safety requirements.