Google wary customers about the spoofed Google Checkout invoices designed to look similar to Checkout invoices, with one important exception: payment is requested through wire transfer, money transfer services such as Western Union or Moneygram, or direct bank transfers. This's a clear scam signal because Google Checkout does NOT support money transfers in any of these ways. (emphasis added)
If you received a fake Google Checkout invoice, you may wish to file a report with the appropriate authorities and/or your regional fraud reporting center -- such as Internet Crime Complaint Center, a partnership between the Federal Bureau of Investigation and National White Collar Crime Center.
For more information on scams in general, see this post How to steer clear of money scams.