Paul,
eBay is a free platform for selling and buying items. No one is forcing anyone to buy anything. If you find a deal then go for it. If you think the prices are way too high, then you have the personal power to vote with your wallet. No one is helpless!
As for selling on this site, I have noticed that many of the offers are EVEN MORE EXPENSIVE than eBay. So you do you want to pay MORE for the same item?
This web site is NOT as organized for selling items as eBay is. By that I mean that the site curator does not get involved if a transaction goes sour. There is no feedback system on this site to warn potential buyer.
This site is mainly to share news, techniques, ideas, and so on about HP calculators. It does include a modest for sale part. Again, those folks comfortable with selling and buying here do so, and those who are not don't get involved.
Either eBay or this site, we ALL HAVE A CHOICE. Each system has it's dynamics, advatnatges, and disadvantages. We pick the ones we are comfortable with ... or none at all.
Namir