Cheating is an inflamatory and harsh term to use, especially when talking about solitary play involving a feature of the game you just happen not to agree with. I don't agree with the use of the arcani, gladiators, the ahistorical Egyptians, head hurlers and other game features, but I don't call them cheating. I don't agree with the AI's ability to hold rebellious cities that a player would lose, but I don't call that cheating either.

The historical period was a harsh and often cruel time, and conquerors weren't above slaughtering and enslaving those they'd conquered to keep order, so it's hardly against the spirit of the game. The Romans, for example, totally annihilated Carthage just to ensure they wouldn't rise up again, sending a stark and brutal warning to other conquered people that they'd better not rebel else they and their family, their friends, their entire city would be in chains or dead. No doubt it was considered by the Romans to be a highly cost effective lesson. They might have been hated, but more importantly they would have been feared.

Due to various features of the game it can at times be impossible to hold a city no matter how big a garrison you use - the AI has no problem of course due to its little advantage. So what is a player meant to do, shrug his/her shoulders when the city rebels and forget about it? They do what would have been done historically, taking the city back and putting the populace to the sword or sending them to the slave markets. Unfortunately a feature of the game is that it only kills/enslaves a set percentage of the population, so the city might still be rebellious, triggering the whole cycle again.

I don't use the technique of selling the city to an enemy rather than just letting it rebel before re-conquering it, but even that isn't totally unreasonable. The technique could be interpreted as your diplomat having just pulled off an intelligence coup, deceiving the enemy into believing they were funding a revolt. Or perhaps he's just a slick salesman and could sell body hair to a Gaul.