I'm not sure what the problem is here, or what people are suggesting they should do:
* Not check tickets? Then they lose out on the revenue.
* Pay an extra member of staff? An expensive option when there is already someone on board who is perfectly capable of checking / issuing the vast majority of tickets, and can give the benefit of the doubt on the others.
The general objections seem to be "but it's not a rail member of staff". That shouldn't matter if they can do the job (and I don't see why a bus driver wouldn't be able to), but seems to be the typical reaction due to the protectionist unions.
There is no problem at all with checking tickets. The problem is that the bus driver is unlikely to have the knowledge of the majority of rail staff, nor the Avantix ability to look up restrictions. Add to that the fact that they will be unable to accept card payments, (warrants? vouchers?) nor sell anything but local tickets, and you can see why people have concerns.
I am not speaking from the point of view of any union, but as a customer. Would I be able to board this bus and buy a weekly season on my debit card?