All too often you find yourself outcompeted by two players seamingly working together (cheating) but not quite sure if they are just temporary allies (not cheating, just being smarter than yourself).
Suggestion. Create a Cheat risk point system based on suspisious activities
1) Playing a lot of games with the same player increases the points. (Does not mean thay are in fact cheating. just means the risk is elevated). Risk point is increased further if these two players often come out on top as no 1 & 2
2) reports from another player obviously should increase the cheat risk points
3) allies who leave their borders unprotected without attacking turn after turn increases cheat risk point. (Remember this can sometimes happen without cheating. it is just a cheat risk behaviour)
4) two players that constantly prefers to attack one player at a time until taken out, but not each other generates a cheat risk point. That is very hard to do without talking/agreeing (i e cheating)
...Etc. I am sure we can agree there are a lot of ways to spot the cheaters.
Haven't thought of all details just a rough idea. Everybody will sometime behave suspiscious in the eyes of opponents and get some cheat points added but some will generate far more and will be the real cheaters. Cheat Risk points could be shown either to all of us players to decide if we want to play or not or as a "secret cheat nummer" alerting SMG to take action or have a closer look.