Resolving props about correct plays

[peps...@gmail.com]

Suppose two players disagree about the correct play and want to resolve the
disagreement in a prop. There are two approaches that can be taken -- OTB
play or a bot rollout.
If players agree to resolve OTB, the prop can be made completely fair.
However, there is obviously a huge chance component. If players disagree
on the checker play, they play an even number of games, alternating sides,
with each player trialling their choice.
A cube disagreement can be handled similarly except that, in the event
that there is a D/P advocate, some of the games are resolved immediately
with a payment of the stake.

However, resolving in a rollout is much more ambiguous. Presumably
XG is used. Are there any established conventions about how decisions
are rolled out, or does it vary widely?
How about, if the difference is ultra-marginal? I think that there's a
standard convention whereby no one pays if the decision rolls out
as ultra-marginal, but I don't know how the marginality is defined.
Is there something like a 0.01 standard here?

Thanks,

Paul