First off, this is just my opinion, to each their own.
I have noticed quite a few YCH auctions that run the same one Your Character Here auction simultaneously across several different art websites. The bids go: an FA user posts starting bid, then the artist themselves posts a higher "bid from [insert other art site here]".

I'm just throwing it out there that I don't like this. None of my YCHs will be run this way. When I post a YCH here, it appears here and only here, and will not be reposted again here or anywhere unless there were no bids at all and the auction was not met. Personally, I just feel that running a multi-site YCH might be seen as a little too easy to pad or cheat the bids. Kinda like imagine if you place a bid on something you like on a site like Furbuy, but then the poster of the auction outbids you with a bid said to be from Furbid, or Ebay etc. Even if the auction runner is completely 100% honest and fair with the bids, I personally just feel that the legitimacy is too hard to see and track.
I won't even run the same one YCH on two different sites as two separate auctions. With differing user bases and user activity count etc where you could have bid for the same image cheaper on one site than another, even that I personally feel will not be fair to you all and will not do.

I know as the artist this may hurt my exposure and cost me chances at higher bids, but in the long run I'd rather appear as fair and transparent as possible than the former.