My suggestion is that items that are available at vendors in the game - such as tools, cameras, quills etc, should have a maximum auction price equal to the cost of them from the vendor.
The reason is that I often see auctions for 100c or 200c items that you can easily get in world from the vendors on sale for 1000c or more - the only reason I can see for this is to take advantage of players who don't know where to get items from.
I've no problem with selling on a tool or whatever that you've upgraded and you want to recoup some of your currents, that makes sense to me, but to be able to list those tools at 3 times the in world price isn't fair, imho.