I don’t use OBO or firm because people are always going to make offers if they just see a price. I think I list games at a reasonable price from the start, but if the market doesn’t think so I don’t want people to be discouraged from offering by labeling my game as firm. I can always accept or politely reject any offer that is given. Labeling a game with OBO seems to show to most potential buyers, send me the most lowball offer as I know I’ve overpriced my game.