Yet, somehow the admin changes the escrow amount randomly (no explanation to OP), and later even refuse to release the escrow at this moment because of OP's reddit post.
This kind of support service is completely unacceptable.
They did actually provide an explanation as to why they deducted the amount, I do not agree with the way of thinking though. They deducted it basically because I had to split the amount in two bank transfers. However those two bank transfers arrived on the same day at the sellers bank account (the next business day after the trade), the split transfer did not cause a delay in payment, so it was no difference for the seller. So I don't accept to have anything deducted from the 13 BTC.
My only fault seems to have been that I was so kind to inform the seller of the split transfer via the message system. He took it up as a reason to cancel the trade, saying I have to pay within 90 minutes. He simply tried to find a reason to cancel the trade.
He should have advertised his trade with another payment method, if he needed the money within 90 minutes, like cash trade, cash deposit for example.
There is no reasonable expectation to receive a bank transfer between different banks within Australia immediately, it is impossible.