Why is it that a seller can post a tracking number? but when you try tracking there is nothing?

[zanadoo_56]

Is it an Australia Post tracking number or a courier, or from overseas?

If it's an AP number you should get confirmation when AP has accepted lodgement of the tracking no.  There can be a delay.

If it's a courier service and you don't know what courier ask the seller what courier is being used. If it's an overseas postal service try entering the tracking details into a general tracking service like 17Track or Trackitonline.

[davewil1964]

Probably too late, 3 months after the fact.