You are right Banjiman and normally the organiser will have sorted that out before the event.

Very often, you get 2 very good performers who are equal billing. A good organiser will work out who would be best opening and who would be best closing based on the audience.

For example, I would put a solo performer on before a band (assuming they were equal)

So Tim in your scenario, the organiser hasn't done their job.

Sometimes you may have 4 performers of equal standing. It's then important to mix the 4 to give variety to teh audience.

Amongst those 4, you can normally work out who would be best to open the evening and work the audience, followed by somebody entirely different in style, etc etc.

If you can't work it out, then you draw for the order.

Just because somebody goes on first does not mean that they are not good. On the contrary. They are probably doing the job for the organiser that works best.