Same old TOL I see!
A point of clarification:
If by "standing behind an accusation" one means "place a very high stakes wager on the veracity of the accusation," then I think they are mistaken. There are any number of things I believe. There are any number of things I believe about certain people, good and bad. Opting out of a high-stakes wager regarding those beliefs does not somehow incriminate me or entail that I am lying. It simply means that I do not consider myself sure enough to place such a wager, or that I am not especially interested in the prize of the wager. So you could say sod's refusal shows
something, but you cannot in good faith say that it simply shows him to be a liar or a coward. The exchange is even somewhat comical to me:
TH: I am a lawyer.
Sod: I don't believe you. Prove it.
TH: I don't believe that you don't believe me. Prove it.
Sod: You're full of crap, else you would have proved it.
TH: You're full of crap, else you would have proved it.