When I was in China, and more serious about learning Mandarin, many of the chinese teachers advised me to study in Harbin, as there it was claimed, a foreigner could learn more standard Mandarin. It surprised me as I thought Beijing would have been the best place, but many recommended me to teach and study in Harbin, if I wanted to speak mandarin properly. Perhaps it is to do with the use of that northern RRR sound, that cannot be so easily replicated by southerners? Met the odd taxi driver in Guangdong, who couldn't speak mandarin well, or if he could,didn't seem to like to have to do so.Perhaps much like some villages in Wales, perhaps speak welsh?