I'm assuming my Flying A sign brought you to post this?... so I will only post my (bias) view.
I ran that Flying A plate on ebay for nearly a month at $640 obo... with no sale. I decided to post on OG because I know not everyone shops on eBay. I also posted the ebay number to let everyone know that it was listed as well.
It was sold at 4pm via PM on this site, while I was on my drive home. I did not get home until nearly 8pm, and by then it had also sold on ebay. I apologized for the mixup, refunded the money, and that was it.
Dave... I personally feel anyone has the right to list as many places as they want (when listed for a buy-it-now price)... as long as you show due diligence in removing it when it sells. and I would guess that many feel the same way judging from what I have seen. Many veteran members of this site & the hobby do the same with ebay, their own site, & this forum.
and the only thing that feeds me or affects my livelihood is my career. that is why I refer to this as a hobby, cause its not a job... I dont need two of those.