Bots are set up by players and the majority of them suck, however I have heard that some programs are getting better, but when FT did a massive bot bust, I went to one of their forums and there were alot of ticked off players who were already down before the shut down.
People program for certain betting patterns and they work best in fixed or pot limit.
If you suspect someone of being a bot, you can search them on opr and they usually have outrageous player patterns that would seem impossible for a human to do.