I am not an expert on insurance but I am pretty sure that liability insurance is not the same as insurance to cover cargo. Any questions of this nature we automatically suggest talking to an Insurance professional. This is such a complex topic and there are so many different types of courier services out there that for insurance purposes you would really have to nail down exactly what it is that you would be transporting. If you are talking about a general business liability policy those are pretty straight forward and relatively inexpensive. I would recommend talking to an insurance broker that specializes in commercial policies. Brokers deal with many different insurance companies rather than just one. I would not go to a stand alone insurance company ie Allstate, State Farm etc. basically companies that deal with normal residential type coverage, house, car, health life are not who you want to go to for commercial insurance.
I use Willis formerly HRH/Charlton Manley.