How is it PR when it's been happening for years and apparently no one knew about it until Robert Jenrick and the Daily Mail teamed up to bring 'awareness' to it.
The zoo never know how many tickets they'll sell on any given day. The ticket price doesn't go up when less people are there, does it? If "these people" spend no money in the café, the zoo haven't lost anything, if they weren't going to visit anyway? They haven't stopped full price people from attending. They aren't costing them money to have there. They've just gained £100 from 100 people (for example) that otherwise would've stayed at home.
As has been said more times than I can count now, all businesses offer discounts in some form or another - Kellogg's discounts on Merlin attractions. If you pay full price and I've got a 2 for 1, have you paid more? Of course not. There is no evidence anywhere - or if there is, people are being very coy with it - that prices increased as a direct result of these offers.