perhaps it has to do with shipping? If its a large or fragile piece that can't be econimically shipped, then depends on where it is. Just a guess.
I have seem sone real odd prices on ebay, avg radios from the 60's going for crazy prices, then the next week sanity comes back. I guess it only take one or better two deparate gotta have it buyers to drive a price up. But it does of course not last.
Of course I never sell anything so what do i know