I don't know if it makes any difference now, but this is how I got it:
Note that spawning the tax collector seems to be completely random. However, although not guaranteed, one can try this method as it has been known to be working with some people. Follow these steps:
Originally Posted by dnv0303
1: You will need to have the Arsenal (bottom area of Constantinople) unlocked, as part of the story.
2: To the right of the Arsenal, is the Mercenaries HQ. Withdraw the money from the Bank here.
3: Head into the gates here into the Arsenal, to the cranes and wait here till money is deposited in the Bank again.
4: As soon as money is deposited, head back through the gates to the previous area with the burned down tree.
5: A tax collector should spawn. Kill him or leg sweep him to get back your money and earn yourself the trophy.
Sorry guys, don't know how to do that copy thing in here. A side note, as soon as I got the money the first time I went inside the Arsenal behind the closest crane & didn't move untill the money was deposited & BAM just as decribed above, it worked!!!