For me, personally...in this hypothetical "if I was a poz top, or a neg btm...etc." scenario or any other combo, the question is always:
"Are both parties making an informed decision based on what they know at that point?"
If the answer to "Are you +/-?" is "I don't know, I was last tested a day,a week, a month, a year, before you were a twinkle in your father's eye", then answer that.
If you're gonna go bare, don't be a coward and try and weasel in another fuck with a guy who'd otherwise be unwilling because of whatever reason. Not worth it, not worth the drama and very much not worth the legal trouble.