In any disagreement, someone has to provide the evidence. Figuring out who - and how much - is half the work.
Placing the burden of proof on the person questioning a claim rather than on the person making the claim.
Claiming something is true because it hasn't been proven false, or false because it hasn't been proven true.
Changing the criteria for proof, success, or acceptance after those original criteria have been met, by demanding additional or different evidence that was not part of the initial challenge. The person retroactively alters what would count as sufficient evidence to avoid conceding the point.
Dismissing counterexamples to a universal claim by retroactively redefining the group to exclude them, rather than accepting the counterexample as evidence against the claim.