I am in the exact same situation now, I live in Australia and have been considering buying a brand new 5d mark 2. On ebay the prices range from 2.3k upwards, in stores the cheapest I can find is 3k.
As others have said, there are no free lunches.
These "cheap" cameras are actually overseas stock, usually shipped from Hong Kong, this mean all warranty repairs must be shipped to HK, which means it will take longer. Some of these sellers offer a "free" warranty repair pick up service, which can help a bit, still, do you trust they will be around when you need the repair?
The big reason I am opting against buying this off ebay now is the tax implications, all the sellers I contacted are not willing to provide me with a "tax invoice" that means that as a business you can not claim GST back and as an individual you can not claim it as a deduction that easily.