What do you call a person who conducts sales by bidding?

In traditional terms, I'd say that would be an auctioneer.

These days, bidders are SDRs, sales development representatives, who do prospecting and lead hunting and then sell them product. Where does the bidding part come in?

When the average proce of a product is determined, whiich isn't too high, and too low, it is determined as the bid price that suits just about most of the prospects out there. And hence the activity carries on.