If you haven't already seen this post over at Blue's News (what's wrong with you? all the cool kids go to Blue's News), you really need to take a moment and check it out.
So some bad news: any hard-coded detection of spin-botting leads to an arms race with cheat developers – if they can find the edges of the heuristic you’re using to detect the cheat, the problem comes back. Instead, you’d want to take a machine-learning approach, training (and continuously retraining) a classifier that can detect the differences between cheaters and normal/highly-skilled players.