Once someone’s made it to the front, you can’t just send them back and tell them to get in another line, for several reasons:

• It makes them even angrier than the people stuck behind them already are, making a scene. If it’s an honest mistake, they feel they’re being put upon. And if they’re trying to pull a fast one, they won’t like being caught.
• Checkout lines are only set up for one-way traffic, so there’s a logistics problem.
• And there’s that pesky “the customer is always right” meme.

My suggestion: Charge a small fee, maybe 10¢, for every item over 15 or whatever the limit is that you’ve chosen. Post it on the sign and treat it like a late fee. If you want, donate it to some charity so people will at least feel better about it.

• It’s an economic incentive to discourage people from bringing in too many items and slowing down the express lane.
• People stuck behind them will feel a little better knowing that hey, at least the dummy with 25 two-liter bottles of soda is getting dinged for it.
• The line can still move forward smoothly.

Sure, you’ll still get people arguing “I didn’t notice I had 16 items!” (Just pay the ten cents already, and count more carefully next time.) And I’m sure there will be some people full of righteous indignation that how dare the store try to charge them for exercising their right as a consumer! It also won’t take care of people trying to handle returns through the express lane, but I expect that’s a less frequent problem.

So…good idea? Bad idea? Some horrible flaw that I missed? What do you think?