In wire transfer fee article (https://support.upwork.com/hc/en-us/articles/211063898) written that additional fees could be applied: "If your bank uses an intermediary and/or correspondent bank, it may charge an additional fee. Please ask your bank about the possible fees."
It's ok, in that case wire transfer should be sent with 'SHA' SWIFT instruction. But! I received two wire transfers and all of them are sent wis BEN instruction that mean ALL of transfer charges are deducted from transfer amount, not only correspondent bank's fee.
So 30$ upwork's fee is not sent to pay transfer fees, it looks like just upwork profit... Wired.