The fact that they contacted you first and are proposing to sell for more than your purchase price are two sure-fire signs of a scam.
Even though they did not ask for any money yet, what they will likely do (we hear of this on these boards so frequently) is they will tell you that they have closed a deal. The "buyer" has paid and there's a huge cheque waiting for you. But, in order to release those funds to you, you need to pay some sort of fee or tax that does not exist.
Once you pay them, they will tell you (if they respond at all) that the "buyer" has backed out or could not get the financing, etc. Then, you are out that money. Do not fall for it!