2) they're not employed to do it (could that include Dad working for Daughter??) No mention is made of payment.
I've never met any diy'er who knows how to do a tightness test, even if he has the kit. (I DO meet a lot of rgi's who don't know how to do it!)
It would be impossible for a diy'er to PROVE he's competent, and of course as soon as he does something wrong, he's proved the opposite.
Shouldn't annoy Mod 10, should it?