Will allah punish people who cheat others? If a person commits sin and ask allah forgiveness and allah forgives that person then where is the justice for the person who got cheated?
Islam says that we have to make amends if we do something wrong against someone else that results in their harm/loss. So as per your example, if we cheat someone out of something that rightfully belongs to them then we should return it to them as part of sincere repentance. Failure to do so results in justice being served in the afterlife when some of the wrongdoer's good deeds are taken away and given to the victim.
Whoever has wronged his brother, should ask for his pardon (before his death), as (in the Hereafter) there will be neither a Dinar nor a Dirham. (He should secure pardon in this life) before some of his good deeds are taken and paid to his brother, or, if he has done no good deeds, some of the bad deeds of his brother are taken to be loaded on him (in the Hereafter). - Bukhari 6534.
In the end, there will always be justice because Allah (ﷻ) is the most Just and Best Judge.
Allah will only forgive what pertains to him only!
He will NOT forgive the right of people (حق الناس ) , if someone cheats, he/she must ask for forgiveness from the one he/she cheated on!
If that's not possible for any reason, he/she must in a way convey/express his/her remorse and tries to make up for it.
Some time, someone does something (cheats on his significant other), but his/her S.O doesnt know about it. Here one must not tell her/him what sin he/she has done as this is a sin by itself and also it will create distrust and may worsen the situation further. so one must ask for forgiveness from God first, then decides not to do that again and take actions to remedy what he/she has done.