The trick to any tax preparation or tax planning engagement is to do the work as if you would have to defend it in an audit. And when it comes to an audit, “Google said I could” is about as defensible as saying “I saw it on TikTok,” “I read it on Reddit,” “My cousin's friend said I could,” or the Twinkie Defense. What you need to defend in an audit and win is substantial authority (and really good books and records, but that is a topic for another day). This article provides some tips for conducting tax research that will get you to the authority you need.

How Should a Disregarded Single Member LLC File a W-9?
Although Form W-9 has some other purposes, a company will usually ask you to fill it out if you are a business-to-business service provider . If you don’t provide a TIN to your customer, they may have to subject you to backup withholding . If it is my company that asks you for the W-9, I am not going to do backup withholding if you don’t send me the W-9. I’m just not going to pay you until you cough it up.
I believe in learning from experience. But it is better if the experience you learn from is other people’s experience. That is why a very large percentage of my tax writing is from court opinions, most often the United States Tax Court. This piece is my own experience.