Deals like that aren't unheard of. Sometimes you just need to get rid of your stuff, whether it's a sewing machine or some other household item. I sold my 6600 on Craigslist at a very good price. I had upgraded to a 7700 and really just wanted the 6600 to go to a good home where it would be used. The person purchasing brought her husband with her, and my husband was at home with me. I demoed it for her and she took a turn at it and we were all very happy.
I'd use some caution as others have mentioned. I would not expect someone to take a check from you unless it's a bank check or is certified. If the machine works and you agree on a price, expect to pay cash.