How about adding a "request" feature? For example, say someone is looking for a Kindle DX hacked to accommodate a USB keyboard. It would be nice to allow him or her to post this request so interested makers could jump on it. Perhaps prices or bounties could be offered by both buyers and sellers?
I actually had this up for a month, and it turned into "well go buy it here (insert link)". I thought it would work out like you are thinking but it turned out a bit different in execution
If the product already exists, the advice on where to find/buy it is valuable. It would be a great boon to visitors, as well as drive more traffic to your site through web searches. One of the most valuable things about Amazon is the reviews which often contain additional info/insights about products, even where to find (legitimately) free ebook versions of print titles, etc.
This suggestion is actually pretty good! Don't be too afraid of loosing customers that way. Most who are looking for this special kind of solutions are most likeley interested in other products as well. And things like these let your site come across as community friendly, i.e. let visitors bond with your site and less likely to run away when something new comes along. The site is a great idea, but try to get more products on board, i.e. troll robotics sites, offer successful kickstarter campaigns a place to sell their "overproduction" units, etc.
But that's an excellent response. If the thing "here" is what they wanted, wonderful. But often it's not exactly what's needed "yea, like that, but I need it to be wireless" so what's happening is you're now facilitating a dialogue between the Maker and the Buyer and that gives the Maker an opportunity to create a product that's exactly what that Buyer and others like him will want.
I'd be perfectly happy - so long as you disclosed it up front - for ou to automatically add your own affiliate code to links like that where you can (perhaps with special handling for people who post links with their own affiliate tracking already). If you managed "the community" right, you MIT even be able to start a culture of recommending vendors for which the site has affiliate deals - so users might selectively choose to recommend Sparkfun or Adafruit (where you've got affiliate relationships) over deal extreme or eBay (where you don't)
