I’m always following auction listings for the higher value 1889 overprinst and often bidding on them too. This 2s6d was listed on Ebay auction ending 06 July 2014 and I found it quite interesting due to the easy to spot and identified overpint flaws, the dot between “l” and “a” and the dot in the “d”. The seller provided a nice high resolution scan of the stamp. 
This looks like the position 1 contstant flaws for this stamp and just checking the perforation comb for this position by eye the dropped/raised holes and wide/narrow perfs all agreed. I’m fairly sure this is indeed a position 1 stamp from the sheet. The overprint has the full oily look which is consistent with this value. Next step for me was to measure the overprint and this is where things went wrong. 
It only measures 12.6 from S – d and some of the intermediate measurements are also slighly out. Looking at the zoomed in version of the overprint some things I pick up that also worry me are the dark frames around the letters (but I’m not sure about this and maybe its due to scanning contrast settings) and also the shapes of some of the letters. My opinion is that this is a dangerous fake overprint on a genuine stamp, in this instance even the constant flaws were forged. This stamp finally sold for USD42.76, less than 7.5% of the current catalogue value of the genuine Swaziland stamp. I hope I’m right 
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