Generally the way people assume their opponent is a bot is you won't see any of the cards be highlighted on their turn, which is what you would expect to see if a person was moving the mouse around to different cards. The bot also tend to make all their actions in the same time intervals. So it will be something like -Play a card - 5 seconds - Play a card - 5 seconds - Attack w/ minion - 5 seconds - Attack w/ minion - 5 seconds.. I just saw 2 players today, using hearthbuddy. SO NOTICEABLE AND OBVIOUS.
True, there should be a human option, or atleast an option making it possible to adjust time inbetween each move.
This is being worked on for hearth buddy 2.0 This has been an issue for bots since day one but got to be a big issue the last 3 months
Random card hovering seems to be the best solution for me so far. By the way, it's funny, when you stay on rank 20 and you're about to concede after win, but your opponent does it before you.