The problem with the part I added emphasis to, is that quite often a company needs to hire a DBA because they don't have anyone who knows anything significant about the subject. So they really can't effectively screen against fraudulent interviewees.

The usual answer I see on that one is, "pay someone to do the tech screening for you". But how can a company know whether or not the person/company doing the tech screening knows their business or not?

I've had technical interviews by people, frequently at recruiting companies, who quite obviously didn't know SQL well enough to detect whether I did or not. Questions like, "why are table variables faster than temp tables", and when I reply that they aren't, and provide details on why, and explain that it's a "DBA urban legend", they start to look like deer in the headlights. I swear, when those people ask their second question (usually, "what recovery models do SQL databases have"), I could tell them that "SQL Server doesn't actually use recovery models. It uses azimuths generated by flux capacitors to power the warp coils for wormhole navigation", and they'd be so intimidated by the reply to the first question that they'd believe me.

So how can a normal small business tell? That's why so many small businesses end up with people who can baffle with BS instead of actually competent technical personnel. See it all the time.