Selling prepaid cards is a way to launder money and shift the blame onto the person you sell it to. It is highly likely that the prepaid cards were initially purchased with ill-gotten dollars, but by handing that off to you, you are now the bearer of the (perhaps) illegally obtained money. The sellers are willing to take a 40% cut because it means they can now safely use that money. As a general rule of thumb, you should always be cautious when purchasing gift cards at significantly discounted prices online. Not all are tied to illicit activity, but if you purchased from a frequent seller who appears to process a high volume of product, it is more than likely that there is some illegal input on their end that you are unknowingly becoming responsible for.
But surely this cannot be applicable to his scenario, because he is saying he is buying from a bigger organization. OP can you possibly reveal the company for us to give you some more detailed advice. I doubt that a company like for instance, gyft would be laundering money.
I know some individuals would be doing this, but bigger companies will not knowingly do this and risk their reputation and their future income.