Our company handles demos of software usually with two people.
The first is the "facilitator" and is almost always someone from Administration or Marketing. These people make sure all the "stuff" is where it should be. "Stuff" can include chairs, tables, coffee/drinks, food, layouts, posters, etc.
The second is the "pilot". The pilot is the person who will be showing off the software, and they are generally either one of the developers of the software, or someone in IT, since generally we demo software that is still in or near the prototype stage. The IT people at our work are familiar with all of the software we produce, so their training generally comes from usage of the software itself.
For us this works well, because the facilitator can start talking about company stuff and promote enthusiasm while the pilot can focus on making sure the system doesn't come down in front of the folks with the money :) In the case of a technical problem, the facilitator can help keep the clients busy while the problem is fixed.
In case you're wondering why we call the second person "pilot", it's because we happen to operate a VR facility, and often do presentations there. Many times the person presenting is actually one of our clients, to a group of their own clients. So they tell the "pilot" what to zoom in on, turn visible layers off, etc. If the demo is a powerpoint or pdf they can ask the pilot for the next/previous slide, or to switch to a video, and so on. This way, our clients don't have to learn our system, but can benefit from presenting on a 22 foot arced VR screen.