Fair enough but have you also considered that some of us might have been interested in it before it was posted on here. Suddenly there's another 35 folk watching it on EB and it's getting pricey.
There are of course differing views about highlighting such listings on forums like this - yes it's informational/helpful to members who maybe looking for something specific, but equally, increasing awareness in this way often drives up the price through increased competition largely to the benefit of the seller. I admit that I have done similar in the past and flagged things up on here that were for sale elsewhere but my view has changed and if I do so now it would only be where something of potential interest to members here was being offered at a fixed price.
On other enthusiast forums (eg military watches) it's often the case that posts and/or links about auction items on external sites are disallowed until the auction has ended, an approach which I think is fair and reasonable.