I am sorry for being the devils advocate here but this does not sound so much like a scam as it does a case of a returned computer. If it indeed was slightly used you should have been offered a lesser price. As the store surely knew it was a returned item which is not usually done with anything electronic due to misuse. My guess would be the person who returned it packaged it very well to look as it was never opened. Scam No! A poor judgement by best buy yes. They should have checked the PC to see it was not used before taking it back. As the above poster said the BBB will help with that if you can't resolve it with them call a news show like help me Howard and they will investigate it to see if the procedures were followed to the store policy and believe that they do not want to hear the company name being sullied on the evening news.
Just my 2 cents.
If it were up to me I would invite all the scammers to a party, The rest I can not say in public forums. I am sure you can figure it out?