I know Amex has recently been advertising Melb Airport accepting Amex, but I was there last night. When I put my Amex into the payment machine, it says, 'Unknown ticket'. Tried it three times. Then put through the Citi Visa and it's fine.
Didn't notice any credit card stickers on the Level 2 machine either.
Didn't notice any credit card stickers on the Level 2 machine either.