US Withholding Tax

Use W-8BEN, keep a master copy. Job done.

Much of the IRS literature is available online  - Google will find it and there is a W-8BEN available for download. The form is self evident and only requires you identify the right boxes to tick and are relying on DTT with US.

The reason most don't ask for it is because they don't know or don't have enough need for compliance. I suspect the company that does need it has a SarBox compliance process in place. Those same companies usually also want customer agreements etc especially if it refers to contracts for some sort of service rather than goods.

The easiest way to get this done is to have the form pre-completed (but not signed) and available online, then use a service like Echo Sign for you to sign and certify sending to suppliers which they should in turn sign and acknowledge. That way you have a demonstration that you have done your bit which also 'certifies' them from an IRS perspective. Done this way, everyone is 'clean.'

Your client should also make sure that either the US company returns witholding tax (that should be possible but unlikely they'll conform to such a request as it may already be part of a US return) or provides a certificate of deduction which you have to use as part of the tax comp and not as part of the pre-tax accounting.

.. about what is required.

A W8-Ben is only required if your client MAY be taxable in the US. Unless it has a "permanent establishment" (see the DTT for meaning) in the US then it cannot be taxble in the US and there is no need for a W8-Ben.

But, hey-ho, if completing the form is the way to get the supplier not to withhold, then let's all ignore the correct procedure!

IF the payer should deduct WHT, consider if the effect of a W8-BEN [or similar form] is (i) to avoid need for WHT, or (ii) to reduce the rate of deduction to 15%.

I say this because with a W8-BEN still I receive dividends from USA companies into my ISA less 15% WHT.