One of the ways we avoid being duped on an auction is looking carefully at the feedback.  If the seller has a significant number of feedbacks, check to see were they feedbacks on purchases or sold items.  What was the cost of the items?  Sometimes a seller will have bought individually a large quanity of $.99 items to quickly and cheaply build positive feedback.  A seller could then start selling big ticket items, several at a time, in a short period of time.  Potential buyers may look at the large amount of positive feedback and expect positive feedback to continue in regards to their transaction. 

Most people leaving feedback do so in an honest and considerate manner.  Sometimes, unfortunately, people give feedback in a malicious manner.  It is the expectation by ebay that if a problem occurs, the two parties discuss the problem first and if unresolved, address through the feedback.  A few individuals ignore the description and speak their displeasure through the feedback instead of with the seller.   Please review what has been complained about and determine whether the displeased individual's concern is valid.  Usually the response gives clues to the validity, as well as, how frequently negative feedback by other people have been given.   Feedback can be manipulated to "get back at" another buyer or seller, but if those who respond, do so honestly, most can see what is happening. 

A word to the wise.  If you are buying or selling an expensive item, check to see if when shipping, you can have the item verified by the shipping company or notary (maybe even with a photo) and shipping persons name, date, time and if return is necessary, a similar authentification.  The reason that this may be beneficial is that thieves will make a very expensive purchase (or a seller list a very expensive item for auction), the item would be purchased, a complaint will occur.  Check the person's name, phone number, address, any identifying information prior to buying.  If something does not seem right, contact ebay security to see if they could verify if the information is accurate.

If the seller sent an inferior item intentionally, it is unlikely that ebay would be able to validate that unless the buyer, when picking up his purchase, opened it in front of the shipper who could write a description of what arrived.  If the buyer is the deceptive one and wants to return the item but sends an inferior item, the seller must insist on clear return photo's with the shippers name, date and time or a notary to do the same when shipped and when received.  Sounds like too much to do.  If you are sending an item worth thousand's and receive a box of no value on return or send a few thousand and receive a box of no value; then finding a way to validate other than using an intermedary that is unbiased may assist you in recourse.  The fight may have to go to court but having an unbiased third party involved may help one receive some justice.