Fake North Borneo Japanese Occupation one line overprints

I have been rather perturbed by the amount of fake material that has been on offer recently on a very well known online auction site. To be fair at least one dealer does describe his items accurately whereas there are others who concocted some sort of unlikely story to make them sound authentic. This is not good for our hobby now nor in the future. If an item looks or sounds too good to be true then it should be subjected to the highest scrutiny. I say this from personal experience.

I got this lot recently, apart from the 4c pair, in the knowledge that they were unlikely to be true. The genuine stamp would have a catalogue value of up to £500 each. However, the 4c pair is most likely to be authentic. The black overprint is somehow much more common on the 4c stamp. Looking at the the pair, one could see slight differences in the inking and less so in the the japanese characters which would be normal in an individually applied handstamp.
The rest of the stamps have fake identical looking overprints which would suggest a modern printing process. Significantly, the individual characters are also a little larger whom compared to genuine looking examples.
Click on the picture if you would like to see a larger image.

I show examples here which I think are the real McCoy even though one can never be entirely sure. They are in violet which are the more common versions. Note how the inking is not so precise and is different from stamp to stamp. Of course I can not rule out that these were applied by fake handstamps applied individually. Those postwar fakes can be very difficult. It would not be easy to reproduce a violet overprint convincingly with a modern printer, I think.
The $2 overprint on the 1c stamp and the Labuan overprints on Straits stamps are rare as hen's teeth and so do not expect to get them for a relatively small sum of money from a total stranger online. I am not aware the Labuan overprints are even listed in the SG catalogue. I could be wrong. The war tax overprints are not so rare and are also frequently forged.
I once saw almost a whole stock book filled with all the fakes I have mentioned at a stamp fair passed off as normal. There are so many around and so are worth little in moneys. There are many rogues out there. I have updated a comment on the Showa overprints. You can read it here.
Expensive JO stamps should ideally be accompanied by a suitable certificate of authenticity. Organisations such as the Royal Philatelic Society of London have access to reference collections where they could compare the stamps. I understand that they also possess an expensive ultraviolet lamp which can show up the differences in the ink that has been used in such overprints.
For collectors who would like to find out more about these overprints, there is a whole series of articles in past copies of the Sarawak Journal. They are available in pdf form on CDs at a very reasonable price. You can order them directly from the Sarawak Specialist Society.