I'm with you that they should mention certified or at least trained professionals (NY does not require certification). I do favor homeowner fixes if the level is just over 4.0pCi/L and they seem handy, though. More than once the cure for elevated radon has been a couple tubes of caulk and a sump cover before retesting. I'm happy to do this, but they don't need to pay me if they can do it themselves. If the level is above 4.8 or 5, though, these simple solutions alone have not worked in my experience and a mitigation system is needed.