I was considering purchasing a camera very cheap on ebay less than a month
ago. I contacted Canon and asked if they would refuse to repair a grey
market camera. They said that they CAN NOT tell a grey market camera from a
camera sold in the US. The only difference is a new US camera has a US
warranty card. If you don't have a warranty card, they will fix ANY Canon
camera for the same cost (cost is based on problem). The person told me that
there is no way to tell if a camera is sold in the US or not based simply
on the serial number. It is the exact same camera and they will fix any
camera and will not charge more for grey market because they can't tell what
is grey market and what isn't.