Yeah, the shelves look pretty nice. I was seriously considering them. In the shelf system the spikes would be just a part of the whole though. Why should Adona manufacture spikes when they can get those for a good price. No one is going to feel cheated that those spikes were used because they are included in the whole system as part of a bigger whole (value added). Even adding more spikes to an existing order at their $22 is defendable since you are providing one stop shopping and one shipping charge (convience = $).
However selling just the spikes alone (which is what both links I gave are) is a little different. In this case as far as I can see there is no value add to justify a higher price. It almost looks like scalping.