Double Red dials on Ebay - info please

[BrooklynsBestest]

I am not making any allegations about the authenticity of this dial (or others that may be posted on Ebay) but while trolling around for something completely different (and cheap), curiosity got the best of me and I did a search for Sea Dwellers... JUST to see what was out there.

I came across this listing:
http://www.ebay.com/itm/ROLEX-SEADWE...ht_1205wt_1114

It's for a Sea Dweller Double Red dial. $125 (US).

Admittedly, my knowledge of the Rolex world is limited. The one thing I do know is that 'regular' Sea Dwellers aren't cheap and Comex or Double Red Sea Dwellers, being classified as rare -- definitely aren't cheap! So I wonder how a lone dial ends up for sale on Ebay if these watches are generally so coveted to collectors.

Is it common to see Double Red dials for sale? Are these legitimate? If so, why aren't more SD collectors jumping on sales like these? Is there any way to determine the age/authenticity of dials like this - especially if it winds up on a watch that someone has purchased later - without knowing the dial came from a non AD seller on a site like Ebay? Does a dial like this affect the value of the watch? Is there a market for Double Red dials or fakes?

Just curious. Thanks, in advance, if anyone has time to answer.
- BB

P.S.
Apologies if this shouldn't be posted in the WATCH OUT section.