it depends how old of a CZ you're talking about. There are major differences depending on year of manufacture. The first CZs, roughly 1500 made, had a round trigger guard, rowel hammer, and the frame dust cover extended nearly to the muzzle and deep blueing. These boast some of the hardest (but no brittle) steel ever used in a production pistol. The next group still have a round trigger guard and rowel hammer. The dust cover was shortened to the now familiar pattern, the steel hardness was reduced and a half cock safety was added. These CZs also has distinctive grips-with kidney shaped rectangles along the back, large stipples everywhere else and a large CZ logo towards the trigger area. After this CZ made major changes to the design. The back strap's shape was made rounder and the tail was lengthened, I've got no idea why as hammer bite was never a problem. To get an idea of the early CZs backstrap look at a Witness pistol as these have retained the original shape. The shape of the slide release and safety were also changed. The next set of CZ75s saw even more changes, the hammer was changes to spur style and the trigger guard was made square. The latest encarnation is of course the CZ75B with the passive firing pin safety added.
Another thing to keep in mind are import stamps. If the pistol has none then it's probably an early model. Among the importers that I can recall off hand are Action Arms and Magnum Research. There was also a Canadian firm that imported them for later sale in the US.
A couple of variations that are out there to keep an eye open for are the early military model, a pistol that supposedly was never made. These sport cobby wooden grips and a lanyad loop at the base of the grip. The lanyard loop is octagonal. These pistols are completely sterile, no serial numbers or place or origin anywhere. I've read about these but I've never actually handled one. The other is a military model ientical to the early CZs except for a lanyard loop.
If it says Made in Czechoslovakia, has a round trigger guard, spur hammer, and extended dust cover the price asked is a bargain. If it says Made in Czechoslovakia and has a rounded trigger guard, rowel hammer and unchanged back strap it's still a good price. Anything after these and you're better off getting a new one.
If you want me to email you some pics of an early CZ75 let me know.
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So many pistols, so little money.
[This message has been edited by Tecolote (edited May 15, 2000).]