EBay + Paypal	Google Base + Checkout	Amazon + Amazon Payments
Listing Fees	$1.20	Free, but you can purchase adwords.	None
Site Commission + Payment charges	5.25% + 2.9% + $.30	2% + $.20	$1.20 + $.99 + 10%
Sale method –	Auction + Fixed price	Fixed price	Auction or Fixed Price
Payment method	Paypal	Checkout	Amazon Payments
Reputation management	3-point – Positive, Negative or neutral	Checkout has a 5-point scale – ratings not publicly available yet.	Rating on a 5-point scale
Dispute resolution	SquareTrade mediator Available for $15 more   Paypal Dispute resolution	Google Checkout	A-to-Z Guarantee
Cost of a $25.00 book sale	$3.50	$.70	$4.69
API/Integration support	Yes	Yes	Yes
Services for high-volume sellers	Powersellers	None	Pro Merchant Services

 

As anyone who has used Google Base knows, the user interface is useful, but hideous and is unlikely to give a viewer a warm enough fuzzy feeling to buy anything. But then, Google Reader started as an uncoordinated ugly duckling to begin with, before it turned into a swan. Also, in addition, the "features, not products" mantra leads me to believe that Google Base is undergoing a major revamp, with tighter integration to checkout, video and mail. I also think that the Google Checkout process, which deals mainly with goods, will be more customizable in the future - and you will probably be able to change the workflow according to your requirements.  I am integrating checkout for a services offering and it would be very useful to us. 

 

Update: Google announced that they are waiving all fees for Google Checkout until the end of 2007, and they announced new features - a coupon creator and email invoice. For those who used the Google Checkout API to integrate - merchant coupon were available earlier, but the interactive version is now available to those less inclined towards programming.