In order to know what is karma to a person in samadhi and how it works for such a person, it is first important to understand also this (most of this answer would be advaitic i.e. based on the tenet that God is One and the Jiva is not different from Paramatma): what is samadhi?
Samadhi refers to the state of thought-lessness with instant destruction of causation and dissolution of the mind. Sri Swamiji Sivananda says in "Raja Yoga by Swami Sivananda":
The Yogi in this supreme state loses all external consciousness, all awareness of duality and multiplicity; he loses even the I-idea (Asmita) in Asamprajnata Samadhi. That is the Supreme State where the Seer (Purusha) is established in His own Svarupa.
There are two (actually there are many classifications) kinds of samadhi, sabikalpa samadhi and nirvikalpa samadhi
Sabikalpa samadhi - This is like sleep. The sadhaka goes into the thoughtless state at times and then returns to the thoughtful state at times. He is like a man who is craving sleep. He differentiates something as 'World' and something as 'God'. He cannot remain completely in the thoughtless state, because the potency of His karmas is strong enough to pull him back to the world.
Sri Paramahansa Yogananda says in Autobiography of a Yogi:
There are two stages of samadhi. In the first, the consciousness merges into the Infinite during meditation. The yogi cannot preserve that state, however, once he comes out of his meditation. That state is known as sabikalpa samadhi.
Nirvikalpa samadhi - This is like love. The sadhaka is constantly and completely immersed in the thought-less state. There is no time when he is not in that state. For him there is no difference between 'World' and 'God'. In this state he moves about in the world like an ordinary man but he is internally completely immersed in the Satchidananda Brahman, or he may choose to shed the body, it doesn't matter.
Paramhansa Yogananda says in Autobiography of a Yogi:
The next state is called nirbikalpa samadhi. In this state of consciousness you maintain your divine realization even while working or speaking or moving about in this world. Nirbikalpa is the highest realization. Once attaining that, there is no further possibility of falling back into delusion.
So what kind of karma affects such a person who has attained the highest state? Does he get affected by any karma at all?
Prarabhda karma is typically known as the in-escapable karma that one MUST GET in one life or another. The sadhaka, on attaining the highest realization, all karmas are now meaningless and ineffective on Him. Some saints say that Prarabhda karma still exists, but Shankaracharya says that all actions are removed, including prarabhdha, for such a state. In Aparokshanubhuti by Adi Shankaracharya, he says (Shloka 98)
And all the actions of a man perish when he realizes that (Atman) which is both the higher and the lower.
Sri Krishna says in the Gita that a yogi who surrenders all actions to Him, Sri Krishna will himself remove all sinful reactions (karmas) of the soul Gita 18:66.
Renounce all dharmas and surrender to Me alone, I will deliver you from all sinful reactions, do not despair.
In this state he MAY or MAY NOT follow the law of karma. Everything He does in this state is only for Divine Will. What is Divine Will, it is that which is not motivated by any personal desires or wants. He moves about teaching others, doing karma for others, showing others how to live, how to love and how to enjoy life.
Sri Ramakrishna says in "Gospel of Sri Ramakrishna" that though this state of Brahman or Nirvikalpa samadhi is thought-less and is like total merger with Ultimate Consciousness, many still 'choose' to come back from that state in order to teach others, or in order to act according to Divine Will:
There are some who come down, as it were, after attaining the Knowledge of Brahman - after samadhi - and retain the 'ego of Knowledge' or the 'ego of Devotion', just as there are people who, of their own sweet will, stay in the market-place after the market breaks up. This was the case with sages like Narada. They kept the 'ego of Devotion' for the purpose of teaching men. Sankaracharya kept the 'ego of Knowledge' for the same purpose.
So in short, there are two samadhis. In one the sadhaka is still under the law of karma, but is partly in control and partly karma controls him. In the second state, the sadhaka has transcended every possible karmic law and debt. The only reason he may still choose to abide by that law of karma (like Rama or Krishna who at during key events abided by the law of karma) is due to Divine Will or will that is not motivated by any personal desires.
So now as for your example, if suppose a man was to be cheated in a business, but before the karma takes effect, he attains the Highest STATE of COMPLETE samadhi. Then if He does return back to the world, then it is upto Him. He may, for example, in order to show others that cheating is not good for others, willingly go through the reaction. Or He may, in order to show others that God is above and beyond Karma law, willingly remove all reactions of that. Thus it is upto God what He wants to do. The one who has realized himself as God and then returns back to the world for the sake of others, is verily God Himself come down amongst us (avatar purush), isn't it! God is above and beyond karma but still he may choose to follow it.