See, enlightened self-interest works against that principle. If you've got a self-interest time horizon longer than 10 minutes, you'll see that it makes more sense to sell the customer something he or she won't regret buying any time soon, or you won't get repeat business and word of mouth. There may be a little bit of oversell, but with the calculated aim of the customer growing into the oversold features.

If, on the other hand, you sell mainly to passing traffic and/or tourists, or from a temporary stall, then you genuinely don't have an incentive to hold back.