I don't let other people use my gear.
In the situation of supporting, "I am leaving after we have played".
Nobody that I don't know quite well will ever touch one of my basses.
I once played a gig supporting a former name 60's musician from Liverpool. His bass player (ex Eurythmics, allegedly) looked at my two Trace Elliot combos - which were already nicely balanced in the PA mix from our mindgame of a soundcheck earlier and he asked to use them.
I was used to a nice low onstage balance. He wasn't and he turned them both right up, so the crowd out front got treated to what amounted to a terrifying bass solo from him, instead of turgid jangly 12-string 60's hits. People were holding their ears.
He was not pleased when I walked onstage immediately and turned off and unplugged the one that wasn't mic'd up and turned the other one back down. On my way offstage, I told him (on mic) he was free to take a break between their songs to get his gear out of his car if he touched the volume again.
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Having said all of that, I DO let people plug into my gear at the weekly jam night. But I have total control over the volume in that situation and take a spare bass for the mortals to use.