Yes. You are right. I think your example has been discussed before. I too have thought that it is very easy to sabotage the chip value of another.

My scenerio goes as follows: I notice a very expensive chip on ebay (let's call it that red $5 Dunes chip that was just sold on ebay). I could very easily steal the scan and make minor changes to it in a graphics program (alter the shade, fill in a ding, add a ding, rotate the inlay so it doesn't line up with the inserts in the same spot, change the background etc). Now let's say I do this several times, each time being different. I could then place a competing ad on ebay showing a dozen $5 Dunes chips in a Dutch auction at a very low price ($100 each, for example). The price of the single Dunes auction would go nowhere (with a dozen going on another auction). I would then be able to steal the single Dunes auction at not much more than $100.

Yes, bad things can be done with scans. However the person swiping one scan to sell his chip is not the person to worry about. The real crook will appear to be legitimate. You will not think that the scan he steals was stolen.