i have a large amount of money pass through my hands every summer and i do not refuse any bills and i have not once had a bank of store tell me my money was fake. i will spend 20 five dollar marked bills at one time is some stores and the clerks are happy to get the small biils. i did have a coffee clerk at starbucks in the toronto airport refuse my marked money but when i told her all my money was marked she did take payment in marked money. now she was a foriegn woman east indian i believe and from watching how she handled money i do not think she was very familiar with the canadian currency (fresh to canada i think). i know if i was in another country other than the usa i would have trouble with their money also so not to blame her for being unsure, but if your going to work in a fast paced coffee shop in an airport you really should know your currency.