First mistake - getting off the moto before we got to the bridge. I should have demanded that he drop me off at the bridge rather than in the middle of a chaotic situation.
Second mistake - talking to the money changers. I don´t know why I do things I know not to do...talking to them only invited other scam artists to approach me. Should have just moved purposefully toward the border.
Third mistake - letting my guard down after the first encounter. I let a seemingly friendly person beguile me after dealing with the stressful situation regarding the money changers.
Fourth mistake - not keeping my eye on the money during the exchange...failed to heed the advice that old cab driver gave me back in Cartagena.
Fifth mistake - not hearing (or having them go off) the warning bells when the guy agreed to accept a barter-type payment (sunglasses) rather than the cash that was owed.
Sixth mistake - not tearing up the fake bill and throwing it away. Should not have let someone else try to pass it along.
Oh well, he got me good...good on him.