There are two ways of becoming a target of blizzard (gathering only).
A) another player actively reports you
B) you start to show up in blizzards heuristic tools
Someone is online 24/7?
Unlikely to be a human.
Online times are either unrealistic or vary too much (noone really farms for 8 hrs after raiding 4 hours, at least not on a regular basis)
You give gold away to random players you are not affilliated with on a regular basis (e.g. different accounts etc).
There are some factors that actually LOWER your heuristic score:
First and foremost: authenticator
Blizzard DOES log you off from time to time on purpose once your score reaches 75/100.
If you log on within 60 seconds using authenticator, your score is lowered by 50. Bots can't grab their iPhone and authenticate
Chatting in /g or /realID and actually participating in real convos also lowers by a huge amount, but only when actively monitored by the abuse team (15 people in paris for the EU realms).
Having BoP raid gear, a huge achievement pool and other stuff a botter would never do lowers by 20.
Last important info:
Let 100 bots pass before you accuse a paying player of botting when they aren't.
That's the rule of thumb within the abuse team.
This info comes from a friend of mine who is a GM supervisor in paris.
I trust him, but can't guarantee for correctness at this point.
Hth