These guns are made to long outlive you and probably your heirs. Their mechanics are relatively elementary, and even with a great deal of neglect and abuse they will operate just fine.
That said, I know where you are coming from. And when I bought my first Smith, I wanted my first revoler to be a brand new gun. I wasn't tied up in the lock politics, so I bought a new S&W with the lock and loved it. I now own more than a dozen Smiths, and all the rest have been used.
And that is because "used" covers a wide range. First of all, a lot of guns you see are barely used. Many have been barely shot. And how much it's been shot may really only matter when the round count gets extremely high and/or the owner doesn't clean their gun. Hickok45 has a video with his S&W Model 29 that he estimates has been shot in the high-tens-of-thousands of times. It looks brand new, and in his video he not only tells great stories of shooting the gun extensively for 30+ years, but it still fires dead accurate and shows little sign of "wear and tear" (except for the cosmetic turn ring on the cylinder and the obvious flame cutting on the top strap, neither of which affect performance). I have some guns that are safe queens that rarely ever (if ever) get shot, and some that I shoot almost every time I go to the range. I clean them extremely well and most folks can't tell the difference.
There is nothing wrong with used guns. (Even new guns are fired three times before you get them). What you want to avoid are abused guns. So if you see a used gun, ask to handle it, and check out a few basic things:
1) Check to make sure it is unloaded of course, and look down the barrel, with a flashlight or phone light if possible. Look for rust or pitting or anything that doesn't look like a nicely rifled barrel.
2) Again, double-checking that it unloaded, pull the trigger and keep it held back. Now fiddle with the cylinder - does it move or shake? Ideally it is locked up S&W-famous tight. Look at where the cylinder meets the forcing cone? Is there a gap? Ideally, no.
3) Now, dry firing slowly, check the timing of the gun. You can google how to do this, but it is very easy and is a simple test to make sure that the internals of the gun are operating properly.
4) Finally, size up the gun cosmetically -- do the aforementioned turn ring/flame cutting indicate heavy repeated use? Has the gun been maintained or does it have superficial dings and scratches (which on steel guns are easily fixed)? Does it come with the original grips, or at least some nice wood or anything better than cheap rubber tires? How about the box and papers the gun originally sold with, are they available?
In my opinion if you can check those four basic things above, then 99.9% of the revolvers you buy will be basically like new. S&W doesn't make a lot of lemons, and those they have made are guaranteed to be fixed. And guns don't really get shot and worn out like you might be thinking, so it's not like buying used tennis shoes.
And finally -- there are PLENTY of older guns out there that are selling literally NIB. S&W new gun prices aren't always cheap, so if you are looking for a good K/L frame .357, for example, and you're looking at $800-1000 for a new 2014 production Smith, you already have the budget for a NIB .357 from 1970-1990 that is more classic, probably made better, has more collectible/re-sale value, and will last every bit as long, if not longer.
Go new, go used... either way -- we want PHOTOS!