A few days ago, I engaged a professional services firm to conduct a valuation of an acquisition that our company just completed. I e-mailed them a signed contract, and was surprised to find that they faxed back a completed W-9 form - without even being asked. I've dealt with suppliers for a couple of decades, and not once has anyone voluntarily issued me a W-9. What a great idea! Let's think through the ramifications.
The normal approach is for the supplier to send you an invoice, whereupon a payables clerk compares the supplier name on the invoice to a list of suppliers for whom a W-9 is on file. If the supplier is new, the clerk mails them a blank W-9 form, and parks the invoice in a "do not pay" file until the completed W-9 form is returned. This means that the supplier is at considerable risk of not being paid if that W-9 is misdirected in transit!
Now let's put ourselves in the shoes of the supplier. In order to avoid this potential payment delay, we need to implement a procedure to ensure that we send a completed W-9 form to the payables staff of the customer as soon as the customer places an order to purchase from us. To do so, the best place to assign responsibility is with the order entry staff, since they are the bottleneck through which all customer orders should flow.
But how to make sure that the W-9 goes to the right person at the customer, or is not mislaid once it arrives there? Consider attaching the W-9 to a copy of the customer order, and send it back to the attention of their accounts payable department, along with a standard cover letter. Since their payables staff may have a procedure to physically store order copies for later matching to invoices, they will probably file the paperwork there, along with the attached W-9 form. If they call later on to ask for a W-9 form, just tell them to look in their own accounts payable matching file.