What is the standard of proof required to call a ball 'out' in unofficiated play?

USA Pickleball Code of Ethics and Rule 6.D declare that all line calls in unofficiated matches are based on the honor system, with players calling their own side of the net. Because court lines have width (2 inches) and the ball compresses slightly upon impact, any contact with any portion of the outer boundary line renders the ball in-bounds. The rule states explicitly: 'If you cannot call it out with 100% certainty, it is in.' A player may not request a replay or ask spectators for assistance. If partners disagree on a call, the benefit of the doubt goes to the opponent, and the ball is scored as in-bounds.