The only way now to buy Arsenal tickets is through Arsenal’s Ticket Exchange: Ticket Exchange | Tickets & Membership | News | Arsenal.com
There will be a window when Red Members can buy tickets and then you can log on to the system, pretty much up until a few hours before the actual match and see if there are any tickets for sale. Have to be quick as they go pretty fast. All electronic now, so tickets come through on your phone. Personally, I wouldn’t buy tickets off another platform or from an individual. If you know someone with a ticket, they can add you to their Arsenal Network, and transfer the ticket to you.