They can. I assume DBAs (Doing business as) folks are the ones that use their SSN. Just real small-time shops.

I think the W9 form says to use SSN in case of a disregarded entity (such as a single member LLC).

> You must show your individual name and you may also enter your business or DBA name on the “Business name/disregarded entity” name line. You may use either your SSN or EIN (if you have one), but the IRS encourages you to use your SSN.

That's straight from the W-9 instructions. You _can_ use an EIN. In my opinion you _should_ use an EIN.

Now I'm even more confused, heh. From the previous page:

> If you are a single-member LLC that is disregarded as an entity separate from its owner, enter the owner’s SSN (or EIN, if the owner has one). *Do not enter the disregarded entity’s EIN*

Edit: I suppose the distinction is that you should have an EIN for your name

Many sole proprietors execute under their SSN. Most will not bother to acquire an EIN.