I think most people expect to get them cheaper here than what they go for on Ebay. You know, the bro-in-law discount.
I think that people expect to get clean, tested equipment, priced fairly, on Geekhack. If the seller is nice and/or generous, then you may find a good deal.
On ebay, sellers are less likely to know what they have and what it is worth, so there will be wildly overpriced and wildly underpriced gear.
If you are willing to clean, test, and/or repair keyboards, you should buy bargains on ebay and expect to put time into bringing them back up to par. If you want something that requires no effort, buy here.