If you sell stuff or services to people, you have to pay for that stuff or services, unless you create them yourself out of thin air.
If you pay some people for stuff or services and then resell them to other people, you could:
* sell them for less than you paid
* sell them for whatever you paid
* sell them for more than you paid
If you sell them for more than you paid, the question arises as to why anyone would pay you more when they could have paid someone else less. There are lots of possible answers: * you bought in bulk but will sell small
* you did a bunch of work to make the stuff/services available
* you did a bunch of work to find customers
* you did a bunch of work transforming the inputs
So, the question about exploitation really comes down to: do you make more profit than can be justified by whatever work that you personally put in?In the case of anyone who makes US$1B or more by selling stuff/services that other people produce, I think it's fairly clear most of the time that they have exploited those other people: that is, their profit (vastly) exceeds the value of the work they themselves did.