There is such a GLUT of used guns out there that dealers are very willing to make deals on older, finish-challenged guns. As long as it is mechanically excellent and the price is right, go for it.
I have seen lots of guns that were just stored incorrectly missing splotches of blue. Nothing else wrong but blue is gone.
If blue is WORN off then inspect carefully for extensive wear. Check rifling, lock up. Some of the older K's are hard to open up. Buy those too. Somewhere in the late 50s S&W changed the direction the ejector rod screws on. The older ones would actually unscrew themselves while you shoot it extending the length of the ejector rod. It would then get very tight to impossible to swing the cylinder open. If you see hacked checkering on the ejector rod of a post war to pre 1960's K frame ... like someone grabbed it with a set of vice-grips, you'll know why. THERE IS A TOOL FOR THAT so you don't hack up the checkering on the rod.
There are collectors and shooters. I have a RM that was a service gun (ordered by a Sheriff in Louisiana in 1935 when new). It has dings from the lanyard, holster wear, a few wear spots of the blue through to the metal and some bumping marks / dings, etc. but is 100% mechanically excellent. I take that to the range to shoot it without worrying about lowering the value of these now VERY expensive revolvers. The other "safe-queens" have never shot as long as I have them.
Hey, if you guys pass some of the 1970s K-38s in single action only, buy them if the price is right. For you guys that don't know in the 70's S&W made a K-38 in single action only. I have seen them in 14-2 and 14-3 but those DASH numbers do not guarantee it is a single action only.
One way to tell is if you pull the trigger, the hammer drops forward about 1/16" while the cylinder rotates to the next stop. It is NOT broken. That is just was a Single Action only does when you pull the trigger without cocking. In single action it works just like any other S&W when cocked back manually.
While the K-38 single action only doesn't bring much of a premium at all now, I feel in the future it might.
S&W also make Single Action Kits for the K series center fire guns. Now, even those K single action kits are getting hard to find when they used to be all over the place for under $100. Now they are $200 or better.