Netiquette 101: To get involved or not get involved

[Zamo]

I was searching a certain online firearms auction site this morning and came across the posting linked below. My interest went from disappointment to outright shock and then on into hilarity. I was initially inspired to write the seller a brief note, and tell him his estimation of the value of this Luger was "a bit" off, but then began to wonder if it was my place to do so.
At what point does pointing out such gross error transcend courtousy and become just plain rude? Oh, sure it's all in the wording, but I was afraid I would be unable to properly communicate in this instance without appearing rude.
I eventually decided to refrain from telling the fellow anything, and rather, post the link over here for all of you to enjoy.
I know prices are always going up, but this is getting a bit out of hand:

Link to amazingly valued Luger