You have to trust a person that will shoot your reloads, as much as you need to trust someone if you're going to shoot their reloads.
Trust is earned.
It isn't only about risk of load failure. It is also about the personality of the persons involved.
I can count on less than five fingers the number of people whose reloads I trust and will shoot without question - in their firearms or mine. And one of those guys blew up a Ruger M77 Hawkeye in front of me -- which is one of the reasons why I trust him (and another witness) more than others now.
Not too many people trust my reloads. But I understand. I color outside the box far more often than the average person. Wildcats, weird combinations, and sketchy old guns are the norm. When someone doesn't even understand the cartridge name, I can't blame them for getting turned off by, "I had to improvise and adjust based on data for [a different cartridge] from Barnes and Berger," or, "all original data was obsolete by 1893, so we have to use A, B, or C now, while maintaining pressure below 26.5k psi."
That being said, there are a few people that trust me without question, so long as they can see me shoot "it" first.
Not long ago, I test fired a long-abused and abandoned Martini-Henry (in .577/450) for the first time. After seeing that I did not die, the person that I was with fired the second round, while fully aware of what it was. A round using 30+ year old brass of unknown history, bullets that he cast but I paper-patched, and a full charge of my home-made black powder sitting under a stack of leather wads.