One for the Postmark People: The infamous BOUI DEP Postmark
For those not familiar with this, the postmark should read BOULDER, a town in Western Australia. The first postmark (22 JN 15) shows what is apparently the final state of the error. The older Western Australia swan (12 JY 10) shows an intermediate state of BOUI DER.
The first stamp is Australia BW 71(1)i, ACSC catalogue value $20 in 2018.
The second stamp is Western Australia SG 140, curent catalogue value £2.