Sometimes for some items if i seach for something let's say a sword in search tab, i see 3 auctions of that sword. If i go Post tab then, and want to post my sword, it's scanning and says scan complete but isn't showing any results like there were no auctions of that sword. Or i shows less auctions then Search tab does.

Likely because they don't have a buyout price. Also, the post tab summarizes identical auctions (with less attributes being considered so more auctions end up being identical).