Is a written commission agreement legally required?

Yes. Under the Real Estate Agents Law 5756-1996, an agent has no enforceable right to commission without a signed written agreement that includes their name, license number, the agreed rate, and the trigger event. Israeli courts have consistently refused to award commission on the basis of verbal arrangements. If an agent tells you a handshake is sufficient, do not rely on that — and do not rely on it in the other direction either: if you believe you owe nothing because nothing was signed, that is correct, but document the situation clearly.