I can't refresh my mind on this point, due to the podcast not being available at the moment... but wasn't there was an effort made to get Clint to answer five questions under oath? He and his lawyer had the questions in advance (maybe not long in advance, but none of the questions were going to be an unexpected surprise while under oath). And the lawyer got Clint out of that one.
I wouldn't take a lie detector either. But if I didn't know anymore about a crime/accident/disappearance than I was already telling LE, and therefore my answer to each of a set of questions, that I can view a copy of, was going to be "No" anyway... then I would willingly go through that process. It seems like such a painless and non-incriminating thing to do. It's possible that that refusal has had an impact on Mr Waggoner's opinion. I mean how could it not?
It's interesting that even members of the same family, who were close to the situation all that time, have differing opinions on what they think happened to Brian. There's obviously nothing that they're "in the know" about that would lead them all to the same opinion.