Not as many bots now, actually fewer than there have been in the last few years due to recent ban waves.
I mean absolutely no offense by this but 99% of the time people think they see a bot it is just a player. Your average bot will perform at a higher level than the average player, especially in bg's. They don't follow people and they don't do crap DPS.
What you CAN look for:
1) You get interupted INSTANTLY, as in too fast to be a player.
2) They have one agenda and one agenda only, whether that be mindlessly zerging and FC by themselves or repetitively running to the largest fight.
3) They don't have the capacity to be smart with trinkets, so if they trinket your CC even though it has DR and will only stay up for 2 seconds, thats a pretty good sign.
4) People who have botted for a long time have their profiles set up better for obvious reasons, if you see that random guy running around a BG intead of mounting, probably a new botter who doesn't have a clue. Report him and hope he catches a short term ban, he's too naive to deserver a perma.
5) If they get hung up on a raid, stump, fence, whatever (you get the point) they tend to back up, run directly to the side and try to go at the path from an angle.
6) They use click to move, run around with it some and that will give you a pretty good idea of how to look for their movement tendancies.
7) And this is the absolutely easiest give away. With a warrior, if they heroic leap extremely fast (same concept as with interupts) and with pinpoint accuracy, you might want to look into the possibility of them being a bot. God knows 90% of warriors don't even use leap, much less use it well.
Their faults are generally in lack of strategy, bots will typically be on the top of the charts simply because they execute flawless rotations and we as humans cannot accomplish that. That being said and as I pointed out above, if they are going kamakazee on the FC room where the other team is turtling, thats probably a good hint. What I'm saying is the issue is that they are getting better and better making them harder and harder to catch. They perform BG objectives, interupt, dispel, trinket, CC (and won't CC you if you have DR, go figure) and do literally any other movement/ability you can think of. Unfortunately you will never catch the ones who are good at it until they slip up and do something stupid like farm ore or get stuck in a weird spot.
Personally I've never understoon why blizz doesn't remove click to move, would wipe out 99% of bots and lets be honest nobody else uses click to move, you would go insane.
Edit: As Aleous said, when farming ore they are easy to spot. It goes back to their singular objective, they will farm farm farm and have no interest in anything else. They fight back if attacked but if you kill them they will rez and go back about their business like you're not even there.
Edited by Amaxas on 3/21/2013 10:22 PM PDT