Kitchen stuff: I'd buy ___ used, but would never buy __ used.
I love shopping antique stores, used book stores, and local thrift stores (and the occasional garage sale) looking for kitchen stuff. I've bought pots and serving dishes and gadgets, but there are some things I'm skeptical about.
Like baking stones and other clayware like that. If it's new, that's fine, but if it's got stains, I'm skeptical. Not so much that I'm worried about someone's pizza grease, but I worry that someone has tried to clean it by soaking it in dish detergent, and that soapy flavor is never coming out.
I'm also skeptical about some applicances. There are some appliances that you can never clean completely because they don't disassemble enough, and those are the ones I'd wonder about.
A cast iron pot you can nuke in the oven, but there's just no practical way of cleaning someone else's coffeemaker.
Conversely, I love finding old cookbooks, particularly at estate sales. I like the idea that I'm getting a book that might have someone's handwritten notes and the newspaper clippings that they saved.
So where do you draw the line?