I thought that other guys response was overly harsh, so here's one of my own.
It's easy to tell if they're a bot. If you message them, they have scripted responses like 'hi' and little else. They have 55hp monks that log into an area, go straight into the mission, farm, log off to stop anti-farming code, log next monk on that account on. That's why in areas like Elona, as per the screenshot, about 80 monks all pop up at once then disappear.
If you see a 55hp monk/warrior pop up in the area then disappear immediately without a word spoken, you know it's most likely a bot. All Arena Net need to do is sit there, write down the names and monitor that player.
They're not even that bright about it. Most of the names I see are asian to begin with to make it even more obvious they're chinese farmers. Up a name pops, second later it's gone. Over and over. I swear Arena Net aren't doing enough about it. Last night over the period of half an hour, I lost count of how many I saw - never less than thirty or so in a single town.
Thirty M/W's in a single town...... now have YOU ever found it that easy to find a monk for your team?

It's glaringly, shockingly obvious who the bots are.