Sometimes by their typing styles, grammatical mistakes, special words that they tend to use a lot, their punctuation, how long their texts usually are and some other hints I might be able to guess who they are. Sounds like you want to design a deep network to instantly recognize anonymous people!

A couple of people on here, and one or two journalists.

Not clever enough

Very Minimally.

I dunno if you mean people I've only seen/heard in real life who I then see in text, or people whom I see in text all the time... if the latter, I can often, depending on the person and probably the message.

not just from one sample, but if I looked at multiple text samples of their I might be able to make a guess

Only Brad Pitt.

I doubt it, but I'm pretty good at spotting catfish.

[08-07-2019]

Yes, I mean 'perhaps' I could, if the 'cues' are all there. tips fedora did you know 'monopolies' are a myth? 'Read it' on thefederalistpapers.org