I’m especially curious about the “find someone who will do it as a service” bit, though. How could I find such a person?
Really depends on where you live. Local classifieds, local p2p selling apps like offerup, facebook marketplace (gross), craigslist, word of mouth from friends/family/coworkers, asking here, or reddit (also gross). Otherwise there's plenty of sites willing to let you ship a switch to them and do it for monies.
As far as vetting anything you find, feel it out as best you can via communication and reviews. I have no recommendations for anything specific unfortunately.