I always ask both sides:
What would it take to change your mind?
A denier will state either ‘nothing’ or ‘complete and utter proof’. The former is obviously useless and the latter simply cannot ever be done in anything but mathematics. You can prove 1+1=2 but you cannot prove anything like, for example, gravity, as they are all models of what we observe.
A true skeptic would answer something like ‘when the balance of evidence points in the direction X then it is more likely to occur’. That’s my position and to-date I am seeing quite a bit of evidence so I think it is most probably happening. Then again I’m a scientist by training and am naturally skeptical of everything.
What I am seeing on the deniers side is something like the argument of the ‘god of the gaps’, splitting hairs more and more finely in order to ‘win’.