99% of the time its betting on lines that are out/higher odds than betfair etc.
Agree with this. Or if a price shortens after you bet it.
People are paranoid about the information sharing thing. There are just too many players online for bookmakers to worry about that stuff. Only when an account is flagged for some kind of issue will it be scrutinized in detail.
Otherwise if an account just bets arbs or steam, account gets restricted and that's it.