Something like this happened to me a few months ago. I got an email saying that a domain similar to one of mine was coming up for auction and they offered to sell it to me outright for $1500. I did a whois and found out it wasn't even registered so I immediately went to Godaddy and bought it for 99 cents.
Two days later I was contacted by someone in Moldova who said they would pay me $80 for the domain. I asked for $100 and they then offered $90. I sent an invoice for $100 anyway and they immediately paid it and I transferred the domain to them.
About a week later, I got another email from someone else who was very emphatic that they wanted the domain for some "big project" and said they would be willing to pay me up to $5000 for the domain. I'm guessing this is part of the overall scam. They convince me that I sold it way too cheap, I buy it back from the original buyer for some big amount thinking I can sell it again for $5000. The wannabe "buyer" wrote me often begging for a reply but I haven't responded.
Since my original buyer has 90 days to get a refund via Paypal by claiming credit card fraud, I'm waiting for it to happen in the next few weeks. If it does happen, I'm only out a buck.
This is why I never use Paypal to sell a valuable domain, but this was just a social experiment for me.
Daniel