I've only filled W-8 BEN forms for personal trading.
As a small business in Poland, I'm issuing invoices to North American businesses with no added VAT (netto==brutto) and a side note that tax is a liability of the party receiving an invoice.
When purchasing services from countries that have "no double tax" treaty with Poland, I'm gathering "certificates of tax residency" which abroad businesses get from revenue government bodies like IRS or CRA.