Yeah, see, my ethics are simple. Do we agree on a price? Yes. End of story. I’m not responsible for that person not knowing the price of the shit they’re selling. (Assuming they are of sound mind.) There’s no need for calculations and whatnot. And same in reverse. If I sell something I don’t realize is worth a fortune, well, tough shit to me. (Of course, my own actions may be mediated by my empathy towards the person selling the item, but I’m not losing sleep over it, that’s for certain.)
Being Mixdenny the mixer collector I have done that a few times. But selling vintage appliances has to be done to the right market with proper descriptions, etc. Just putting “Hamilton beach mixer” in the title isn’t going to generate much interest. Actually very few HB mixers have any real collector’s value. They are generally "users’ for a vintage kitchen.