I think the problem is that people conflate accent and dialect. Accent varies from region to region when people use standard English. Vocabulary and grammar vary very little, and guessing nationality online can be tricky. If someone with an average educational background cannot use the vocabulary and grammar of standard English (as well as their own dialect, perhaps) then they are probably not a very capable person, and wouldn't be ideal for a white collar job. The older they are, the truer that is.