Read the specifications as one connected system.
One feature can affect several decisions. Added equipment consumes payload; water and propane add travel weight; electrical loads affect shore-power and generator planning; and doors, ramps or service windows change workflow and structure. Ask for actual ratings instead of estimating from appearance.
When a trailer will be used for regulated work, show its proposed floorplan, equipment and utility documents to the agencies responsible for the final operating address. A sales listing is not a guarantee of approval in every jurisdiction.
For transport, provide the exact receiving address and disclose gates, grades, overhead limits, surface conditions and unloading constraints. Inspect the trailer and paperwork at handoff and record any condition questions promptly.