It seems like the simple solution is to just give them a loss if they do not show up for a called match within X minutes.
IMO it's better to NOT worry about...
- whether or not this is "disrespecting" the tournament, or people
- how this makes other people feel (or "looking like a fool")
People have different reasons/issues that come up that may or may not be valid.
Keep it simple, and NOT emotional -> not here for your match -> this is the consequence.