How much verification before a broker accepts a power of attorney, and does the forwarder get a say?

The broker is right. The POA comes from the importer of record, executed directly, not passed through a forwarder. ID on the signatory. Form 5106. CBP publishes a page on validating a POA; send the forwarder the link. Two things go wrong when you take less. Importers send a POA they signed with a different broker and think it transfers. It does not, it is a contract with that broker. Or somebody strikes out paragraphs and expects you to file on it. Sign it clean or the shipment sits.

From the importer's chair. We have no traffic department, so I sign what the broker sends, within reason, and I keep the signed copy with the date and the name of the officer who signed, so an auditor can see who bound the company and when. The one time our lawyer struck out two paragraphs, the broker returned it unsigned with a courteous note and we started again. Two agencies at my border, same shape of document.

I see the buyer's side. A US customer ordered a rattan set large enough that the parcel needed a formal entry with her as the importer, and the broker rang her asking for an identity form with her social security number on it. She refused, the parcel came back, and I paid the return freight too. So take the broker's list seriously: a private person who has never heard of a customs broker will not hand ID to a stranger on the phone, and the goods go home.

There are two questions here. First, whether the broker may insist on direct execution, ID and the identity form: yes. The power of attorney binds this broker alone, so one signed elsewhere is beside the point. Second, whether the forwarder's view carries weight: he is not a party to it. Brokers are now held to verifying all this, hence the recent executive order on enforcement. Have an authorised officer sign, attach the ID, and treat the forwarder's opinion as a scheduling note.

Under the UCC, and I offer this as the mirror rather than the ruling on your US filing, a customs representative acts directly or indirectly, states which on the declaration, and must produce the empowerment on request, so a careful representative verifies the signatory before the first filing. The one place the practice differs is that the representation type is itself a declared data element here. A pharmaceutical client's lawyers taking weeks over every paragraph is, I can confirm, universal.