As for the OP's comments: yes, it is fairly widely known amongst banknote collectors.

As a general rule of thumb, on eBay and off: don't buy expensive coins from China, and don't buy expensive notes from Singapore. The coins are likely to be fake and the notes are likely to be doctored.

There are people based in Singapore who buy cheap, low-grade examples of scarce early notes, including Australian notes. They then clean them, iron them, dunk them in bleach and otherwise horribly abuse them to try to improve how they look on-camera. Then they sell them on eBay for far more than what they paid for them.

With a bt of research, it's sometimes possible to track down where they got the note from originally; just look for low-grade notes in places like the Nobles auction catalogue, and watch for the same serial numbers cropping up for sale from Singapore. The old eBay coin and stamp forum (now deleted) had several such examples posted in it, as I recall.