If you fall for the bait and sell something for $2000, you'll receive a check for $3000. The perpetrator of the scam will then claim that a mistake was made and ask that you refund $1000 via money transfer.
So you send $1000 via money transfer, which cannot be stopped… and in the end when it finally clears, the $3000 check ends up being a fake.
It's an old fraud that uses technology for a clever new bit of social engineering.
These messages are being sent to website contact addresses and are including the site name in the body of the message. This results in a message that feels almost personalized and might potentially lower the guard of the recipient.