I really cannot stand that either. It seems rather opportunistic and expensive.

I remember seeing plastic bag vending machines at LTN and felt a bit offended that they had the nerve to charge £1 (or was it £2?) for it, especially because those who would be caught out would be infrequent travellers. With frequent travellers, they could say they should know better, but it's blatantly opportunistic to do this to infrequent travellers.