Quote ="Jeff the God of Biscuits"Ticket prices as noted above, but, they will NOT be selling concession tickets on the day at Salford, just full price tickets. SO if you want a Junior/Student/OAP/Disabled ticket you have to book in advance.'"
I think the message was (or at least should've been) that you can only pay £18 at the cash turnstiles on the day.
Juniors/Students/OAPs/Disabled CAN pay on the day, but will have to queue at the ticket office to buy a ticket, which can then be taken to a ticket turnstile. As this takes a while (and Juniors/OAPs/Disabled may well not be up to the wait especially if it rains, as the queues for tickets are not covered) it is strongly advised that those want a Junior/Student/OAP/Disabled ticket book in advance.
Hope that clarifies things, see you on Sunday!