An auditorium is a place of learning. You might want to start by checking the degree of soundproofing. You could then check the availability of equipment - is there a blackboard or flipchart, for example, or a video projector? Auditoria for 50 people or more will need sound amplification equipment.
A classic training session works best with an absence of tables, a loose configuration of chairs, and a flipchart. Training sessions often last for more than 3 hours, so you might want to make sure that beverages are available at the venue (in the form of a water cooler, or perhaps a kettle).