A customer experienced a problem with his Canon 7D, it would not work on e-TTL even with a dedicated flashgun.
As the flash was a Nissin, I checked the camera with canon 580 EXII and found that it had the same problem but would fire on other modes. I looked carefully at the shoe and noticed that the four pins which transmit e-TTL information were not connecting to the hotshoe contacts. It was possible to slide a piece of paper between pins and contacts even with the gun locked on.
I told the customer the camera would have to go to Canon for service, was it still under guarantee? Yes, came the answer but I bought it in Dubai for ½ the price of a camera in the UK.
I think we know why it was so cheap....................