black market currency trading

kids on the street in this part of vietnam often ask for English coins "for their collection". haha. whilst lurking in the dark alleyways of Hoi An, I got to see the backend of this -- a bunch of kids sold all their sterling and australian coins (about five GBP worth) to me for vietnamese currency at 27000VND/GBP, 13500VND/AUD (pretty much rates I guestimated on the spot - UK rate better than Yahoo's 29200 but Australian rate worse than their 12100). these are the same kids that want to sell you little trinkets such as whistles and necklaces (buy two, get one free for "happy hour" as they put it - no matter what hour of the day it is...)