How do you decide between a scummy player that is town and a scummy player that is real scum? Do they have different tells to you?
I am still working on that one, but I've had some early possible successes (one can also be right because of luck, and can misattribute 'a reason' for something going right when that 'reason' had absolutely no connection - that's how one becomes superstitious about something).
In my first game, BM42, I managed with a huge amount of work and interaction to figure out that Superblackcat, though super Scummy, was almost certainly Town (later proven that he was Town). How I did so wasn't 'tells' per say, it wasn't 'oh, he said this, this, and that - thus he is Town not Scum'.
More what I did was pretend to be him. I made the assumption that -everything- he said was true, then I pretended that I made every single one of his posts, and tried to figure out why I made them. Why I reacted to what I reacted to, why I said what I said, what I meant when I said what I said, why I didn't react to what I didn't show a reaction to.
I made a 'model' of that player in my head, reconstructed from his actions in game, then I questioned 'it' and as Superblackcat continued to post, I compared it against his new posts. Making it wasn't easy - it was possible to do because Superblackcat had posted rather frequently and had interacted with me extensively while I was paying a lot of attention to him. That model let me see Cat as yes, super Scummy, but as Town-Scummy not Scum-Scummy - and suggested several differences in how he would act if he really were Scum and helped me believe that he probably could not behave as he was if he actually was Scum - that had to do with how he handled pressure and what he responded to and didn't react to.
But nothing so simple I could boil down into a list of 'tells', no. I believe any such list would have to be made anew for each player, and would have to change as that player changed.