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Do retailers ever stock goods just to make other goods sell better? 
That happens all the time. The best situation for this to happen is when you have several products, each a bit better and a bit more expensive than the other, and you add a new product which is the cheapest. That gets people into the store to look at the cheapest product, and then you show the the next more expensive which is so much better for only a little more money, and the next more expensive which is again so much better... You might not sell any of the cheapest product but it helps you sell the others.  Also happens the other way round: You add a really expensive item, unaffordable for most customers, that is really, really nice. Then customers look at it and you show them that for half the price they can have something that is almost as nice. The expensive product increases the amount that customers think is "the right price" for that kind of product. A customer might think that $2,000 for a diamond ring is an awful lot of money, but if you show them another ring for $5,000 then suddenly the $2,000 doesn't look that expensive anymore. And if it is almost as nice as the $5,000 ring, you sell a lot of rings for $2,000 because you had the more expensive ring in the store.