Vincent is correct, you can't really get a correct representation of CMYK (subtractive color process) on an RGB screen (additive color process), especially with certain colors like green.
That said, most quality commercial printers will/should provide a printed color proof of some sort before printing the whole run. Definitely check with your printer (or have your client do it) before printing! It's a very standard request; In fact, many printers won't run the job without someone signing off on a printed proof.
If you're having them printed through an online company (much more common these days), you can still get a printed proof mailed to you, but in my experience, many of the online companies just expect you to go with whatever you see on screen. For less important jobs, this may be fine, but I wouldn't trust it.