I have used Google Checkout countless times both as a seller and as a buyer and their service is fantastic. Every time I sent in questions to their email hotline someone actually replied quickly -- AND with a direct, helpful response that did not sound like one of those automated responses from PayPal/eBay (responses that fail to even address the questions asked). I generally use GC for personal clients/off-eBay, MP transactions, and occasionally overseas eBayers who don't have PayPal-confirmed addresses and for whom PayPal is not an option (as I absolutely do not take PayPal when it's unconfirmed address, just cannot risk it). GC conducts manual screening on all transactions, requires ship-to address to match credit card billing address....and yes, when they spot potential problems, they DO reject the payment (I've had a few buyers' payments rejected before), so it's not instantaneous like PayPal where they accept anything and later have sellers deal with the problems, chargebacks, and scams on their own. Buyers also have buyer protection -- (1) from the required tracking (sellers are required to provide proof of delivery and input the tracking # after each order), and (2) from their credit card company, which is basically how buyer protection works on PayPal anyway.
I'm completely with Foxy on this one. I have used Googlecheckout as both a buyer and seller and have had no problems. And, I like that they do fraud risk checks to make sure the credit card is not stolen, etc. My sister actually invoiced a lady yesterday for 2K and she is in Canada and Google denied her payment THREE TIMES. In this case, the buyer is legitly having problems w/ her Mastercard, but I'm glad Google actually denied it. Can you imagine her paying w/ Paypal, my sister shipping out 2K of my niece's clothing out and them reversing the payment AFTER the buyer already got everything?!
I hope that Google does add a contact number for help, but I have only had to contact them one time (as a buyer) and I received a clear response within a few hours. And, like foxy said it wasn't some copy and paste junk that Ebay sends.
As a seller, I just make sure I submit the tracking information via the order as soon as I ship the item. And, it has saved me a ton of hassle as far as International buyers are concerned. I don't have to worry about "confirmed" addresses and nobody has ever questioned my use of it. I direct them to www.googlecheckout.com if there is any confusion and there is a tutorial there as both a buyer and a seller.
And, yes Ebay does not permit the use of Googlecheckout b/c that would mean loss of more money for them. However, Ebay doesn't really do anything for you as far as helping you get your money back if it came down to a claim anyways. Your best bet if you are scammed is your credit card company.