Here’s a similar question that was posted a number of years ago: https://www.theyeshivaworld.com/coffeeroom/topic/relying-on-a-heter-of-someone-else
I actually asked my Rav about this question. He holds that a dishwasher cannot be kashered. He told me that as long as my friend has a psak from a reliable Rav, I don’t have to worry, and I can rely on the psak he received.