I don't think OP has come back to this thread to make clarification to his question by attempting to guide members so he/she could get a near solution.
To clarify, the service charges you say, $100 USD, to locate a product, in this case its .002BTC that you're looking for. You technically paid for the service and not an actual purchase of bitcoin, is the service provider then allowed to transfer you the located product?
I will attempt a response from this point. You see in a contract agreement, you don't try to vitiate, change or renage from the terms of the contract. If for instance, your first agreement was to locate a product for you, it stands as that and you are suppose to pay for the service fee.
And for whether he should transfer btc, I would say no because you have to pay up or pay for the btc.