So basically you did agree upon $2900 but once you factored in the exchange rate and added on the HST you came to $3785, correct?
If so, it is merely a matter of miscommunication, no harm was intended. The buyer was getting a good price at even $3785 and to let it go over 10%+/- is too bad.
Best to you both and remember, no one ment to harm anyone, just a miscommunication, it happens, take a deep breath and close it guys!