Is what the questioner did, by pursuing a woman whose goods the seller refused to buy, in order to offer to buy them from her, considered forbidden religiously and customarily?

If there is no mutual agreement or consensus on the price, then it is not considered "selling over another's sale" or "bidding over another's bid." Therefore, the man's action is not forbidden. The prohibition of selling over another's sale means that one tells someone who has bought an item during the option period: "Cancel this sale, and I will sell you something similar or better for the same price." Or, it means that the two parties have agreed on the price and only the contract remains, whereupon someone offers more or offers it for less. As for bidding over another's bid, it is when the owner of the item and the interested buyer have agreed on the sale but have not yet concluded the contract, then another person tells the seller: "I will buy it." All of this is forbidden after the price has been settled, but before that, it is not forbidden.