One good reason might be the inflated prices people pay on Ebay versus
on AM. I've seen people pay more for a used item there than a new one
costs. On Astromart, you'll (usually) end up paying a reasonable price,
and deal with a fellow astro enthusiast who's a damned nice guy.

I've never had a bad buying experience on either, but I do feel better
about
buying on Astromart.