Forget about fraudulent sellers and conmen for the time being. This is about honest sellers who, in trying to protect themselves from clueless buyers, seem to overdo things. As an example, here's a Return/Warranty policy by a seller with hundreds of feedbacks and a high positive percentage (I've broken it into 5 sections to insert comments) :
1. "Product will be replaced if product is returned in unused condition & original packing...."
Comment: The buyer cannot test the product if he does not open the package and use it at least once.
2. ".....within 10 days of invoice date....."
Comment: A two-way shipping will often take more than 10 days. It would be more reasonable to require the buyer to ship it back within 10 days of receiving the product.
3. "....Buyer will have to send the product to us at his cost If product is defective. All shipping and handling charges for exchanging will be borne by the buyer only..."
Comment: If the product is defective, the buyer should NOT have to bear the cost of returning, handling and re-shipping.
4. "....The returned merchandise is in the original sellable condition including packaging , accessories...."
Comment: The product cannot be in the original packed condition as it had to be opened for checking and/or testing.
5. "....Any shipping and/or handling charges on the original order cannot be refunded in any case....."
Comment: Same comment as for the third section.
This seller is most probably an honest one, but he failed to look at his terms from a buyer's point of view. This is just one example. Similar conditions are laid down by many other sellers. Such terms should be imposed only for cases where the buyer changes his mind about wanting to buy the product, and NOT for cases where the product is defective.