Faisal, I worked directly with FiberStore's engineers to determine the optics and mux needed for my use case. They recommended the mux and the optics for the 3km distance. You can always buy stronger optics, but that is not point I am making. I provided the scale and scope of the project and they provided the BOM to deliver the required service. When the equipment failed, FiberStore refused to honor their return policy and issue an RMA until we threatened legal action.
Same sales scenario with OSI Hardware.. They provide the BOM with passive muxes and 10km optics and it works with no problem.
In this scenario, I can definitely blame the manufacturer. No to mention the terrible technical support that they offer.