Some Australians have reported that they are being asked to show documentary proof of the stated income on their Statutory Declaration at the Australian Embassy in Bangkok.

March 26 2017

The Australian Embassy has clarified that if you complete and are signing a Statutory Declaration claiming an income amount in support of a retirement or other visa, you are not required to provide proof of that income. It should be noted that it is an offence to make a false declaration on a statutory declaration

It is the same in the US Embassy in Bangkok.  They are notarizing your signature, not verifying the accuracy of contents of the document.   

 

Of course perjury is a serious offense.