Can wire transfers be reversed by the sender?

Answer 1

Not always.

In US it works like this: paying bank sends a message to beneficiary bank (ie, receiving bank), requesting the funds back. Beneficiary bank contacts the beneficiary and asks them if it is OK to debit their account. If beneficiary agrees, beneficiary bank will pay the funds back to the paying bank.

If the beneficiary bank does not agree, payee is out of luck. There will also probably be hefty fees involved. So be careful when wiring money.