That point is disputable. Basically, at some point in the past one of us started using Amazon as a valid source for availablility checks. No way to determine who or when, but it did happen.
The admins had a discussion about disregarding Amazon Marketplace as a valid source a few months back. One was for, one was against and the third abstained. :p

But will you count eBay as well then? Because most of the Amazon sellers have an eBay store as well - they're not selling new items really and none or few of them are actual proper stores. It's really a bit confusing.

Also, watch out with some stores selling old games: some sell represses which are of dire quality. I have 3 such games which are useless since they're bootleg prints without manual. I discovered that they were fakes because one CD had a virus from 1998 on it when the game was released in 1996. Dubious eh? The second had a corrupted data file and the third had files dating to 2003. Really sucks because I collect originals, not useless reprints. :notrust:

We're not going to count eBay under any circumstances. While Amazon has some semblance of stability, the eBay is in a constant flux with no single link to a source being viable in long-term.