Robert, Another difficulty is that eBay sales are often like buying
the proverbial pig-in-a-poke. It's difficult to know what you're
buying, unless you know exactly what the condition is. There's no
substitute for seeing an instrument with your own eyes, and hearing
it play with your own ears, and that may be difficult to arrange in
the time span of an Internet auction. I'd never spend over $1000 unless
I either knew and relied on the seller, or would spend that amount
whatever the condition (a bargain).
On the other hand, I'll bet that a lot of potential buyers do watch
eBay. I myself faithfully scan through anything with "organ" in the
name. I have no time/ability to travel, and eBay provides exposure
that my local dealers cannot match. And one may always correspond with
a seller after the auction has lapsed.
As to Gem Roller Organs being more suited to eBay, you're correct.
They are common enough that there's a selection, amateurs often "find"
them and offer them for sale, and the price does not prohibit buyers
taking a chance on a poorly-described organ. I'm always amazed at the
"Rare, One of a Kind ..." descriptions. (Likewise the rollers, which
the manufacturer also called "cylinders". <grin>)