Someone wants to use Western Union to buy my laptop, is this a scam?

Where did you list your item? Craigslist mentions that wiring funds via western union is a scam. Check out the "avoid scams and fraud" link on their website. If it is listed on ebay, I would use paypal and not ship until you get paypal confirmation. If I am not mistaken, there is also some small level of protection for both the buyer and the seller since ebay controls paypal and I don't think you need to use ebay to use paypal.