As long as you're the first one to sell goods, yes, then flip the start player card over to the "?" side to indicate it won't change hands again this phase.
This is not correct. The start player card always changes hands when goods are sold (unless the seller is already owner of the card). Flipping the card is only to indicate that there has been a selling action that round (if the card isn't flipped, it moves clockwise the next round).