Question on ebay bidding?

[Kels]

You know how a lot of times the people who put up items for auction on ebay don't get a good profit out of it? This is due to the fact that people who are bidding have the chance to pay less than the normal amount for that item. At the end, if the final bidding price is really, really low, then it doesn't seem as if the person who put that item up for auction is really getting anything out of it. So why do they put stuff up for auction? Are they able to cancel the whole order if they don't get the certain amount of money that they wanted in the first place? Thanks in advance.