I'm not sure whether this has been suggested before, as none of the search terms I used brought it up.
In some of the places I've been before that had auction houses or other systems to allow players to sell their items to other players without direct trading, there was a database within that auction house where players could view any of the items available in the game, whether or not there were actually any for sale. Something like that within the Spiral Knights auction house would allow players to view items they may wish to purchase in the future without having to use what is essentially third-party software. (While SpiralSpy is an excellent tool, not everyone can use it and it does require an additional download.)
It addition, I've noticed while buying and selling that many items have wildly divergent high and low selling prices, and there's a lot of guesswork in pricing them; if something is not currently in the AH and no one who has sold it before in the Bazaar has posted the selling price, it can be difficult to choose a starting point. Some items, like weapons and armor, have a fairly easy starting point for pricing, as it's easy to calculate the worth of the CR, CE, and materials used to craft it. Others, such as costumes and accessories, are a bit more difficult; if it's been awhile since the AH has seen one and there are few to no established selling prices in the Bazaar, sellers are often loathe to publish asking prices, while buyers are loathe to make bids, each wanting the other to put the first number on the table. It's natural behavior, really.
So what I propose is that the database not only allow you to preview items not currently for sale, but also include non-wearables and track sales data so that the average selling price for each item can be seen. Some items that have never been sold on the AH would still be difficult to gauge and would still simply have to be priced at whatever someone was willing to pay for it, but I think the economy would benefit from a record of sales trends for specific items. (Honestly, I wouldn't complain about seeing graphs included that track average sell prices over a month or year or whatever, but beggars can't be choosers.)
I've made some edits to the interface to show what this might look like in the AH. If the graphs were included, there would obviously be more buttons down at the bottom with the preview option; probably in place of the sell price information already shown on the menu listing.
Existing auctions already influence how people set their prices, but a graph showing price trends or a list of sales on a searched item would make the auction more of a market than somewhere to dump off stuff to sell so you can derp around elsewhere as the seller. The reason prices may vary so far apart is because of variation in the people who post those items; some people think/want their item is worth more than it actually is, so they make a derped price. When it times out or someone gets it for a lower minimum bid than they wanted it is their fault for making the price jacked up. For people who sell below the local prices, their items tend to be eaten up quicker. People like paying less for the same thing. Jerks like me craft some derp item with a derp UV, see someone has a high price on the same thing, and post it for less.
Stuff about a notice board for the market.