I'm happy for the folks that can spend 2.5x the used price to avoid the risk of used gear. I, on the other hand, have only been able to have a taste of high end audio by buying used.
Yeah, I've gotten lemon gear. But overall through the life of the hobby there's no question I have saved over 50% of the new budget by buying mostly used gear.
I agree with the advice above that the best protection is getting to know the seller. For any significant purchase, I invest my time in ongoing dialog with the seller. Not only does that "make friends" and make the transaction more pleasant, but you can get a very good sense of the person, their knowledge and treatment of gear, and ultimately build trust with them.
I also buy a lot of used gear from Andy at Saturday Audio in Chicago. He stands behind everything and the gear is thoroughly checked out. He's swapped out speakers for me when something was amiss. This is the type of dealer relationship you will also want if you are building an ever-evolving system.
One thing I would say is that buying some components from a smoker household may not matter, speakers are big and right in the room and pick up (and release in your house) the smell of smoke worse than most other components. I remember having to wash some ML panels in my shower to make my room livable.
Used gear, and navigating and negotiating...that's part of the fun for me! I have met a lot of really nice people, all walks of life, all layers of society. You'd be surprised what gear some guys who make $40K per year actually have!