I agree with the comments on the value of time and expertise. For many of us on the list making an HID Thor is simple, but most people have no idea how to do this. I just did a 50w Thor mod for a friend who just does not have the time or desire to learn about HID systems......where you buy parts, what reasonable prices are, how you might stuff the thing into a flashlight, which flashlight has a useable reflector, compatible power supply, how to wire it up, etc. Now if I were selling this light on ebay I would certainly expect to make a decent profit.
All of that said, I think it that it might have been in the seller's best interests to have explained in the auction description that this is a stock flashlight that has been heavily modified. The risk in not doing so is that the buyer might see a stock Thor after the sale, perhaps feel he got a bad deal, and then slam the seller with bad feedback.
cfb
p.s. I have a Matsushita ballast that is about three times the size of an Auerswald ballast and I don't think it would fit inside a Thor. There are some big ballasts out there!