Selling an item that is not in his possession through profit-sharing (murabahah) or payment in advance (salam transaction) or by hiring someone to sell it in return for a fee
If the customer wants to buy hardware that you do not possess, you can make a deal with him in one of the following ways: 1. Acting as a proxy in return for a fee; 2. A profit-sharing transaction (murabahah); or 3. Payment in advance for items to be delivered at a later date (salam transaction). Each of these is explained in detail in the long answer.