That does suck and a lot of people are taken in by this scam. If I don't see the dvd listed on commercial websites like walmart or bestbuy I don't buy. More people need to read what tvshowsondvd.com wrote about the piracy problem.
http://www.tvshowsondvd.com/newsitem.cfm?NewsID=3608
You can also report those websites and try to get them shut down. If they are not in the U.S. it won't help though.
http://www.mpaa.org/anti-piracy/contact/index.htm
http://www.rcmp.ca/html/intellectual_e.htm