Transactional Services

This page lists API-based services for listing products and/or conducting transactions. What I'd like to determine is the best fit for a web site that manages the transaction of art sales. It needs a) a way to store product listings & inventory and b) a way to conduct the transaction. Of course, these can be custom built, but all the better if there's something easy and existing. Ideally, it can also be used to list products that are sold - so that a gallery can be created consisting of both sold and unsold work that uses the same infrastructure.

Amazon Services
http://www.amazonservices.com
Upload your inventory, it gets listed on amazon, sell it, and you ship it. (Amazon also has a fulfillment option where they do all fulfillment after you mail them your inventory). $40/mo + referral fees of 8-15%. Pricing here. Also have a WebStorefront option where you create your own store using their templates.

Amazon FPS allows you to develop a payment solution as an intermediary. But doesn't manage your product database, which is the advantage of the solutions above.

Ebay
http://developer.ebay.com/common/api/
Their API-listing service is called Ebay Trading Web Service and it allows you to add an item to Ebay's database with these attribute fields. Listing types are: Chinese Auction, Dutch auction, live auction, real estate ad, basic fixed-price, stores inventory, and personal offer (listed here).  The big problem with Ebay is that each listing maxes out at 120 days. There's no way to list a sold-item - or to have art for sale for a good long time.  They charge an insertion fee + a final value fee.  Details here. The other big problem is the insertion fee. This is just not a practical solution for an intermediary like an art seller.

Yahoo Shopping
Doesn't seem to have any APIs of interest. There are no listing services. Although they do have a stores product that lets you upload products via a spreadsheet. Seems funny that they wouldn't have an API for this.

Google Base
Allows you to submit info about anything via an API - including products. Which then ties into Google Checkout to do the transaction. Automatically listed on Google. 2% +  $0.20 per transaction. More info here. This rocks.

Current thoughts: for micropayments for digital objects, use Amazon FPS. For product listings and other transactions, use Google Base.