> If the candidate did not disclose his salary history, the obvious assumption is that it is not a positive, and the candidate will get a lowball offer.

I disagree that this is the obvious assumption[1]. Even if I were true, it seems to me like your prior is all lowball offers are the same. They are not. If a candidate was underpaid, an uninformed "lowball" (from prospective employers PoV) would be much higher than if they knew the candidates previous salary was about half of their budget.

1. My salary is above average, but not an outlier,but I will not disclose my salary history before getting an offer. I will not disclose it after getting an offer, even if it's too low for my liking. The only number that matters is the one I am willing to accept. If you share your salary history, you may be lowballed an not even know it. "Anchoring" is a well-studied phenomenon - anchoring on your past salary may leave you underpaid relative to the rest of the market (or your colleagues).