You may suspect a che@ter for many reason like staying online all the time or getting maxed out bases in minutes, it's possible for people to stay up for the 6 hour period, I've done it as well. It is also possible to get a maxed base in minutes. However if you suspect che@ting or if you have evidence of it then please send it to support via in game settings (cog icon) ---> Help & Support ---> Conversation button on the top right. Give all the details you have of the player as it will help. Support will get to it and take the appropriate action.
In many cases support can't give you the result or action taken, this does not mean no action was taken.
Same goes for reporting an exploit - or you could pm staff or a mod on the forums.