Seeing this topic, I tried to find an "valid" example qualifying rebluing (for this topic only, I have no interest acquiring it). Here is a perfect example, so called "conehammer" (where is cone? but that's just a given name, not important)
http://www.gunauction.com/buy/121201...ish-no-reserve
Here is why: (1) no blue left anyway; (2) it was not buffed heavily; (3) this variation is very common.
But this one's condition is atypical. Usually guns lost most blue inevitably have pits, rust, fair bore, or mismatched parts, etc. I guess this one has some thin blue in the past, but most likely the blue was not in great shape, or lost some blue in concentrated area so it looked very unbalanced? One owner erased the blue in chemical way and left in "all-white". God knows. Anyway, now it's qualified for rebluing, IMO.
However, if the whole thing had no s/n, don't reblue it. It could be a Mauser prototype pistol. Of course, this one is just a regular production instance, no worry.