Goodwill doesn't pay bills.

From bits I've heard from BA staff I know, it's now a case of doing no more than you have to. Give an inch, and they'll take a mile, expecting that extra 15 mins unpaid you did by default.

I had a look just now at check-in wages for one company, so there might be variations.

30hr part time contract @ £9.67/hour.
Thats about £290 a week before deductions.

Some are offering a bonus at present, so possibly 50p-£1 an hour on top of that.
They may get more hours than that, and at present probably will, although in quieter winter periods, those hours could drop (could be offset by people naturally leaving, so more hours need to be covered?)
Shift wise, it's not all a nice 9-5, weekends off.
It could be 3:30am starts, late nights, 15hr shifts, 4hr shifts etc. so if you've a family, seeing them could be difficult, and a lot of people don't want their lives completely dictated by varied shifts (even though they may have known what to expect initially).

I've been on a few training courses in my time where 12 are expected, but you're guaranteed at least 1 person won't show and a couple more won't make the second day.