Many are not cheating. Let me share my experience.
In level 5, I already had over 500m money.
I am level 17 now. Until now, I spend usd one dollar as supporting nordurus.
Friendly reminder:You have to earn as much as money in transfer market in lower level. Otherwise, you will lack of money to expand seats from level 12 onward.

Money:
Competition prize is not enough. You have to consider how to get money by other means:
- free transfer player: it is always 3 star. Bid at last 2.5 seconds (avoid war bid) And then sell immediately. Don't buy old player, only buy age 18-19. You can earn several millions every day. If he is a faster trainer, you can keep or even train him.
- sell player: keep him in 99% to next season. And then sell him (duration: first week, time: EU night). He is 79% who is useless to you but he is very attractive to lower level managers. You can cross the finger to view the bid war.

Green/red pack:
- watch the video everyday to get green pack. It was 100 in the past but 30 now.
- make sure you have at least 15 red packs. Whenever player is hurt, use them immediately before next 6% recovery time.
- attend every match to get the pack. If it does not need big win in a match, change pressing to low when 2:0 or 3:0
- join FA match

Token:
- download the apps to get some tokens regularly.

Player:
- only buy fast trainer, age 18 or 19
- always keep the player number to 21-22 in your team. Their total values will be increase everyday. Train them everyday and completely used up 48% recovery.
- sell him in age 21 or 22
- progressively change all players to fast trainer
- progressive change all player to age 21 Max

Training:
For fast trainer
80-> 100%: approx 75 greens
100->120%: approx 100 Greens
It is no need to appoint special coach
Special technique: 1 green = 1 point ( corner and free kick specialist is 40 points; if the player has St when selling, it will be welcome to many managers and bid war is expected)

Since it becomes 30x free videos per day, the money increment will be slower than before. But if you follow the above hints, your finance situation will still improve over time.