I would have thought that the problem might be in the use of "Indian".
If you were implying that the behaviour of one of your customers was typical of a race of people then by the Oxford dictionary definition, that is racism ( The belief that all members of each race possess characteristics, abilities, or qualities specific to that race ). This, from your post above, seems to be what you are saying explicitly, i.e. that "every single one has been trouble".
If you were telling a story in which the fact that the protagonist was "Indian" was core to the story, then I'd argue that it wasn't racist. So, "my customer asked me if I wanted a cup of tea today and when it came it tasted of cardomam (then again he's Indian, so I should have expected it)".
My experience is that some Asian customers are trouble and some are wonderful. My experience is also that some British customers are trouble and some are wonderful. It's intriguing that, to the best of my knowledge, I haven't read a single post from you beginning "Today one of my white customers..."
Vin