Shkreli's schtick was to buy out or control pharma companies that had a monopoly and jack the everliving fuck out of the prices. He had some programs for uninsured people, but he would milk the insurance companies absolutely dry, which gave him some wild profits.
This made a bunch of powerful people absolutely enraged, as he was basically publicly bragging about jacking the ever living fuck out of the prices. Pharma companies do this but Shkreli would publicly say it and tell the truth that basically the other companies were doing it while pretending to be good people, and he was only being honest about it. Poor people were pissed because they were told they couldn't get their drugs (I'm unaware if the program that allowed uninsured people to get them for cheap was real or not), and the rich insurance people pissed because he was basically he was bilking them.
So they went back and discovered one or some of his other early enterprises weren't profitable, but that he had used money he made off his later pharma enterprises to pay back his earlier investors.
In trial, his investors testified they were happy with the situation, lost no money, and would invest with him again. But they still convicted him for fraud, even despite the 'victims' themselves did not believe they were defrauded. It didn't help that Shkreli is probably one of the most profoundly unlikeable people you can possible listen to, unless you're not bothered to hear a hyper-capitalist be honest about how they do business.