Professional Catering

I hope you don't mind my question, I am a professional event manager working medium size events.

I have searched and searched online with no answers. I am based in the UK, but I see the rules in respect of reheating are quite the same everywhere.

Are wedding and event caterers just using chafing dishes to reheat food?

I'm seeing lots of mobile event caterers with hot food serving from the table, no ovens and it appears they do not have enough hot holding boxes for all of the dishes they have.

If they are reheating at the table before serving, is this safe and more so is it common?

Can anyone tell me if this happens a lot, and if so what should be happening instead. Presumably not all carry a mobile oven when there is no kitchen facility.

Any replies appreciated. Thank you