Fake error note : Malaya British Borneo 1961 10 Dollars

One thing about collecting error notes is that it is fraud with many dangers. We had one such case recently.  A collector who recently acquired a piece of famous "kerbau" 10 Dollar error note ("kerbau" is Malay for buffalo) and he asked me to take a closer look at it and let him know what I think. Here's the high resolution scan  :

Malaya British Borneo 10 Dollars 1961 Obverse - Fake Error
Figure 1 : Malaya British Borneo 10 Dollars 1 March 1961, Pick #9

The bottom right serial number appears to have been over printed i.e. the "9" has been over printed with a "0".