Like Stevie 'Fifth Official' G diving in the box whilst miraculously looking at the referee at the same time, you can guarantee that there will be people happy to try and cheat in an online game.
Cheating in FML is obviously going to take a different form to other MMOs, since there are no walls to make invisible so you can shoot through them, and paying someone to sit and kill Murlocs for 3 days won't help much either. But as I've said before, there are loopholes, and one of the biggest parts of the beta test has been to try and root out as many as possible of these.
The most obvious and open form of cheating is simply to look up players in the FM database. This is a route open to the majority of FML players, and one that is abused. There's little we can do - the main thing to remember though, is that the majority of FMLers will also own FM08, so it's open to all. Also, most people will know that Cristiano Ronaldo or Carlos Vela are good players in real life... So the advantage is limited - especially since I don't think FML uses the FM08 database - I'm sure I remember hearing in the early days that it was a modified database, with the 'playing field' levelled a bit...
Also bear in mind that a combination of Wage Demand/Acquisition Fees and the inability to sell a player for 7 days after he has signed prohibits rapid exploitation. The skills system will also limit the number of players you can see when you first join up, so not all players will be available to all new users. The loan system, also, was particularly abused - now it is pretty watertight. Measures like these really help to level the field as much as possible.
Cheating opportunities tend to be limited, since we all have the same tools. We tend really to be looking at exploits - things like top ranked sides setting up unofficial 3 team competitions, with a draw seeded by world ranking meaning they played a lower-ranked side in the final for a guaranteed profit. They get eradicated very quickly.
Other forms of cheating have been harder to spot - and that's where I, and the other mods, come in. When something smells fishy, it really stands out for all to see, and it usually gets reported very quickly. There's been a good few people removed from the beta for abusing exploits in the game, rather than reporting them - cheats stand out a mile off in FML, and won't be tolerated, even after retail. But in some senses those people who have been removed were our most valuable testers - each one gone is another loophole shut.
People coming into FML have to recognise that they are joining a real community; the other people in that community are worthy of respect and honesty. Anything else, as they say, just isn't cricket.