Exhibition costs include stand space, travel, accommodation, marketing collateral, staffing costs and much more.
So, my advice might seem obvious; but you need to turn up on time and make the event work for you.
So why did this HE stand lack staff after an event had started?
You could argue traffic, or a lot of other reasons, but really it often comes down to poor planning. If this was a one off it would be one thing, but every event I go to has stands left unattended, staff arriving late (often curriculum staff I grant you .. but were they well briefed?) and opportunities lost.
If staffing will be an issue then either don’t book it. Or if problems occur closer the event have a back up plan. It might be sending staff from other departments, the use of student ambassadors or bringing in external people to help (try one of the FHE recruitment businesses; they often have FHE trained people that can help at short notice.
Clearly the latter is not ideal but a person with some background, that has been briefed by phone and is capable of taking contact details that you can follow up quickly is much better than an expensive empty stand.