Under your specific carrier you have the option to select negotiated or list rates in most cases. Look under Account Settings.
Some Carriers (e.g. UPS Freight) do not give us the ability to pass in a switch for getting such rates, so if the option is not there this will be the reason.
Bear in mind that if you are using the staging/sandbox server then you will not be receiving your negotiated rates (and are quite likely to be receiving higher than list rates aswell). We do not recommend using sandbox for production usage as results can be erratic.