Google Checkout is banned on eBay and can lead to your account being suspended.
You cannot even use a custom checkout which accepts payment by Google Checkout.
Please see the following link and expand (show) the 'Some Examples' section: http://pages.ebay.com/help/policies/accepted-payments-policy.html
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Violations of this policy may result in a range of actions including:
* Listing cancellation
* Forfeit of eBay fees on cancelled listings
* Listing cancellation
* Limits on account privileges
* Loss of PowerSeller status
* Account suspension
Payment Services permitted on eBay:
Allpay.net, cash2india, CertaPay, Checkfree.com, hyperwallet.com, Moneybookers.com, Nochex.com, Ozpay.biz, Paymate.com.au, Propay.com, XOOM
Payment Services not permitted on eBay:
AlertPay.com, anypay.com, AuctionChex.com, BillPay.ie, ecount.com, cardserviceinternational.com, CCAvenue, ecount, e-gold, eHotPay.com, ePassporte.com, EuroGiro, FastCash.com, Google Checkout, gcash, GearPay, Goldmoney.com, graphcard.com, greenzap.com, ikobo.com, Liberty Dollars, Moneygram.com, neteller.com, Netpay.com, paychest.com, payingfast.com, Payko.com, paypay, Postepay, Qchex.com, rupay.com, sendmoneyorder.com, stamps, Stormpay, wmtransfer.com, xcoin.com
</quote>
Basically PayPal is an eBay company and they don't want to loose thier business to competitors. Officially they say that Google Checkout has not got a proven track record that consumers can trust.
Thats my opinion anyway