I gave an explanation on how it could be done, I didn't say that was the way it was done.
Using personal trainer can also turn a low player into a 9* player over night, but that will cost tokens.
Its possible the guy is cheating, but it seems to be common place that people throw the cheating card out on other users without actually having any proof.
I posted a screen shot the other day of a guy who had -9.02K Tokens - and would happily say I feel he is cheating as I have found what I would call is evidence to back that up. If you have evidence to back a claim of cheating up then post it - but otherwise, its wrong to accuse without fact.
The fact remains that I could turn my team from being 6* to 9* within the next 10 mins if I wanted because I have enough tokens farmed and saved in my account. Anyone looking at my team before then after could then scream "Cheater" at me, but I wouldn't have cheated.
Some people do spend a lot of time power training players to get them to 9*. My first 3 players I got to 9* were all done by power training. It took time but I got them there. I've since come to the conclusion it isn't worth my time/effort - but to some they think it is.