Certainly. A basic Mafia technique is examining the past play of the person you're suspicious of, then looking at whether their current play is more similar to their play as scum or their play as town. There is also wide knowledge (at least online) of moves that are generally "scummy," such as congratulating the doctor after he or she successfully protects, as these moves have been determined to be commonly used by scum. Of course, all of this is constantly evolving, since once something is generally known as a scumtell, advanced scum players avoid it. Further, different things are tells at different levels of play, which tends to make the game much more complicated than my above description might indicate.

That said, I think it's certainly possible to do better than chance-- my own record, at least of games that I can remember, is 4 wins to 1 loss, all as town (I have yet to be scum in my recent games).

Further, there are some situations where certain tactics have been determined, over wide periods of play, to be dominant, and applying these strategies gives you a very high chance to win. For instance, if the town has a doctor and a cop (and knows this) and also knows the scumgroup has no roleblocker, the best strategy is to stop voting to lynch, have the cop claim, and have the cop constantly investigate while protected by the doctor. The scum must then start hitting other targets in hopes of getting the doc. A truly advanced doctor will then, knowing the scum is doing this, not actually protect the cop but instead protect other members of the town in the hopes of blocking the scum's pseudorandom flailing, but a truly advanced scum player might anticipate this and try to kill the cop instead-- so there are mindgames all over the place, but dominant strategies are still known.

Generally, I feel like Mafia-- at least online Mafia-- is a rather good rationality exercise. I could expand this to a top-level post if there's interest.

I don't know how well it works in games with only 1 scum player, but with at least two just the fact that there are two players who know they each have a partner changes their behavior enough that the game isn't random. There's also some change in what people say just because each side has a different win condition, although again this is less true with just one scum player.

As just a simple example, when you're playing as the scum it can be really hard (at least for me) to make a good argument that someone I know is a normal villager isn't, which can be enough for another player to deduce my role.

I just had 4 games with the same 5 players (setup is 4 town 1 scum) that all ended in scum victory. Random lynching should yield only 53% chance of scum victory. 0.53^4 seems low enough that this is likely a case of better than random.

The players in this case were new to the game with the exception of myself (and after the first couple games I was constantly night killed). I was going to say that this seems to suggest that scum is stronger in newbie games, but then I realized I have no data to draw this comparison with. :-(

Unfortunately I play mostly as a diversion on a private site, not on mafiascum or epicmafia, so they aren't as out in the open as you'd like. If you want I can link you to a recent newbie game that I was in on mafiascum, but the number of replacements makes it a little hard to follow and it's not exactly anyone's best play either.