This usually goes for all telcom and networking equipment: When you plug the thing in, they device will preform a self-test, aka POST. All the LED's should come on and a couple lights might flash. If you have a manual for the device, look to see if there's a list of error codes.
But if you're selling it, you really should check each port to see if they work. There are several easy ways to do this. You can use a crossover and plug it into one port and then plug the other end into all the others and see if the link light comes on. You should then hook two computers up to afew random ports and see if the switch will pass packets.