I'd buy used if the price was right -- and I could handle the gun, check the trigger, see the general condition before taking ownership. That said, I've not seen many used Stainless CZs for sale.
The Stainless CZ, while having the same grip (ergonomics) as the standard CZ, has a slightly different frame with an extended beavertail, ambi-dextrous safties, and (I think) a reversible mag release. Those are nice things. But if it's just feel you like, other CZ options are also good. Be sure you're getitng the level of GLOSS you like, too. I love the matte finish, and don't care for the highly polished stainless; others go the other direction.
I've done a lot of transfers (buys and sells) via internet connections and have only been burned once, and that was a scald not a burn. (Something wrong with the gun was easily fixed.) If you are dealing with folks who have a known good reputation, as can be found on sites like this, it's generally a good thing. Be warned, however, that SHIPPING CAN BE VERY EXPENSIVE, and if it's not included in the sale price, find out what it will be. (FFLs can ship via mail, private parties can't ship directly by mail -- and Priority Mail with insurance [shipped to your local FFL] is a fraction of the UPS or FedEx costs.)
