I went to Wal-Mart a few weeks ago with my sister to pick up some trading cards. (I like to check both Wal-Mart and Target, since they have slightly different selections.) I had picked out one deck, and a set of three boosters, and got in line behind two people. The first person was finishing up getting checked out, and an older woman behind her was moving her stuff up to be checked out. She put her coupon on top of her paper towels, which was probably not the best idea, since it slid off the package, and onto the belt. It then was sucked under by the belt.
The cashier noticed that the coupon was missing, as did the woman. The cashier started looking around for the coupon under the counter, under the register, ran the belt around a few times to see if it were stuck, and then checked under the register again. 5 minutes of searching for the coupon went by. The older woman was getting a little impatient at this point, and tried to stop the cashier by saying, "It's just 75 cents. Forget about it." (Hinting strongly at, "Please, just ring me up so I can leave!") She repeated this a couple of times, but the cashier didn't pay much attention.
Several more minutes go by and the cashier is still looking for the coupon! o__o I can understand wanting to find it for the woman, but there is a point when it needs to be let go, especially when the customer doesn't even seem to care anymore. It was at this point that my sister poked me and motioned for me to go to another line, as the cashier was simply not checking the older woman out. (She was still re-checking every nook and cranny for the coupon!) The older woman looked very tired, and anxious to leave at this point.
Edit: (As a side, ALL of the other lines were backed up, as well. The one I unfortunately got in had an actual issue that was holding it up.)
It was well over 10 minutes before that cashier finally gave up and started to check the older woman out. She held up the line for that long to look for a 75 cent coupon, even after the woman said she didn't care about it! o_X I'm pretty sure there is a fine line between "going the extra mile" to make the customer happy, and "being obsessive about it," which makes many customers unhappy.
TL;DR: Cashier holds up the line for over ten minutes looking for a lost coupon, long after the woman whose coupon is in question tells her to stop and just check her out.