First, everyones evaluation of a gun being clean will vary. Just filthy to you may look perfectly clean to me. I don't consider a stainless steel revolver to be just filthy unless the top strap is near fully black from front to rear and the outer diameter of the cylinder is covered with smoke residue and has patches of precipitated lead on it.
Standard practice for S&W is to load a round in every other cylinder position and test fire the gun. Now on a 686P that technically isn't possible so I'll bet that they just shoot 3 rounds. That will smoke up the face of the cylinder around 3 chambers and will also smoke up the frame around the barrel. It will also leave evidence of being fired in the barrel and forcing cone. However, that evidence can be removed pretty quickly with the proper cleaning solvents, which IMO is M Pro 7 and nothing else. I have not found ANY other gun cleaning solvent that works as well as M Pro 7, compared to Hoppes it's pure magic. BTW, it's also expensive at 40 bucks a quart but I value my time enough to pay for it.
If they actually had to fire 50 rounds, and I happen to have my 620 which has exaclty 50 rounds fired since it's last cleaning. You'll have a cylinder face that is mostly black with a slight hint of stainless still showing. In addition the underside of the top strap will have a black streak above the B/C gap and be grey to yellow gray from front to rear. In addition the recoil shield will be just starting to show a bit of smoke residue around the firing pin bushing. As for the frame, around the barrel it'll be showing patches of dark gray to near black in some spots but will also be showing stainless areas that are nearly clean. Finally, the exterior of the cylinder will just be starting to show a patch of precipitated lead that will come off with 5 or 10 strokes of car wax on a paper towel.
Now, as noted, on rare occasion S&W will shoot as many as 50 rounds through a gun in the event the sighting isn't to spec. or it has other issues that need correction. However, IMO that is actually rather rare. Fifty rounds will leave a revolver obviously dirty, not as filthy as 200 rounds but dirty enough that many will clean the gun.
Now, if you want a somewhat good indicator of a gun that has seen a lot of shooting the thing to do is check the recoild shield for permanent marks left by rounds bouncing on it during recoil. I have a model 620 with perhaps 2500 rounds through it and the recoil shield is showing a slight bit of shine at every spot where a round would contact it.
Another area that may provide a bit of a tell is the recess formed between the top of the barrel inside the frame and the underside of the top strap. That's an area that accumulates residue and it requires the use of a dental pick or similar tool to remove it. If you can see daylight here, someone was either extremely thorough in cleaning or you have a gun that wasn't fired much.
Finally, in regards to Buds cleaning up a used revolver and re-selling it as new. I do NOT think that this is very likely at all. They do a lot of business on the net and doing something like this would get around and cost them business. In addition, at retail there isn't much of a price difference between a brand new 686P and a lightly used 686P, probably only about 50 dollars. That isn't enough to cause them to try and pass off a lightly used gun as new.
IMO what you got was a brand new 686P that needs cleaning. No surprize there, I don't know of any gun manufacturere who cleans a gun after test firing it, at most they pack it in shipping grease and box it up. Fortunately, S&W isn't shipping over salt water by ship so you don't have to deal with the nasty shipping grease that some manufacturers use.
