There are a handfull of sellers that are listing the "regular" Canonet G-III's for the $275-$325 range. They're the same people as the $600 black ones. No one ever bids on them, as the current going price is ~$120-$150 for a fully CLA'd Canonet G-III. I've seen two black ones sell for ~$270 in excellent shape. Of course, people are buying them for the "rare" color, so it has collector value.
The $600 black Canonet sellers are the ones who make eBay a bad place. I also buy a lot of used digital P/S cameras to fix and re-sell. A camera that I know is worth $100-$125, people are listing for $275-$300. They're hoping they get a sucker who doesn't know you can go to Best Buy and get a better brand new camera cheaper.
It's quite sad IMO.