I think OP has a point: we re now in an era where most earbuds do not have the large, plastic piece that fits on it, but rather the plastic is making contact with the inside of the ear.

I also have personally now cleaned my earwax from the little foil that guards where the sound comes from..! It's kind of gross to share such a thing, right, but I know that anybody who is getting longevity out of their earbuds will have done the same... Plus these are mine, only mine, and the only other person who shares them at all with me is my wife...

So, I would not be excited to buy second hand earbuds and owuld likely personally sanitize them even if I had bought them from a store where they were sanitized already. I would not so far as to say I would not get the earbuds. If they are a steal and quite new, sure, I would... But I totally understand the OP's sensibilities here.