Can someone explain this?

[tornado shanks]

Seller A and Seller B (me) are both selling the same item. We both have the same buyout price, the only difference is that mine is posted with a lower bid, yet his still appears first in the list.

[Basemath]

hmm probably cuz you're not sorting them by highest/lowest bid, rarity, or level. Click on one of those, once or twice, to make the items sorted by cheapest first, and yours should come up first. Usually anyone who searches the AH will have sorted them out by lvl or current bid to have the cheapest come up first.