Beware of false and true "attack" combination
Today we went to buy an iPod for my son.
The shop where we bought the iPod failed to neutralize the
sensor/sticker in the package that causes the alarm to go off at the exit from the shop. So it sounded when we left, but since I knew that I paid for it and the guys in the shop simply didn't pay attention to it, so we just walked away.
And here is the interesting part of the story.
We went on to visit several shops, in each shop the alarm went off on our entry, then the sales men would check us, find out that it is the iPod from another shop and then - just forget us. It seems that they never even thought to check us for the second time when the alarm went off on our leaving the shop. We could've taken the whole shop with us and they wouldn't notice!
This reminded me of something that I heard once.
This technique is often used by the crooks. They let you check something, let you see that it is OK and then take it back for just a second - to switch for something else or to reduce the amount of cash for example. When they hand it back to you - you will not double-check it since you "already checked" and feel sure that it's OK.
So, do not hesitate to re-check!