We all hear of stories about dodgy moneychangers (ps Don't use Wayan (long hair balding at the front) at Kumala mini mart next to Café the Sands in Legian unless you like a challenge) but you do sometimes feel for them.
We used Nasir at Cristal Dewata on Jalan Werkadura near the Jayakarta exclusively and found him to be of the highest standard, Money is counted out to you, he sits back, you count, when satisfied he takes your notes.
On our last day he asked if I could help him, an English tourist whom Nasir described as 'dark' asked to change a $500 US travelers cheque, he identified himself with a British passport with a serial no GB 269-014-824 using the name Thompson. Six weeks after the transaction Nasir's boss informed him that the travelers cheque was a forgery.(I saw the banks reject slip and the travelers cheque and the $60 US dishonour fee). The sad thing for Nasir is that typically your boss in Bali holds you responsible for the debt. Nasir probably will take 11 months of no or minimal wages to make up the debt.
I'm not sure if any forum member has any advice to offer Nasir on how to recoup the money. If they do please pass the info on to him. His phone is 0361 761 970 or drop into his money change, leather goods shop in Legian.