I am not a dealer, but.....I would have thought a rolex was worth at least 30,000 new and a second hand one perhaps 10,000
As another poster mentioned, It depends alot on the model. Then there are considerations like what the secondary market is doing regarding especially desirable models and say, especially desirable models with desirable early serial numbers.
In the end, some used Rolexes can cost more than new ones of the same model. Likewise, for say, older "general" models one can buy used- no, I mean ahhem, "pre owned" examples for say what- 3-5k?