Use your common sense when it comes to price. Of course you might want to get a good deal, and a bit of a discount can be a realistic expectation depending on the situation, but if someone is selling you a Louis Vuitton watch for an obscenely discounted price, it's probably because he's selling you a fake watch. If you're serious about buying a luxury timepiece, you've got to be willing to shell out the cash, or else you definitely run the risk of being sold a fake.
Check out the Louis Vuitton website and find the model of the watch you want to purchase if you can. Take a look at all the distinguishing features of the watch so you can compare and contrast those to the watch you're interested in buying. Make sure to do your research. The more you know about the brand, the less chance you have of falling into the fake-watch trap.
Hold the watch in your hand. Check to see if it feels heavy. Real Louis Vuitton watches are made from quality metals, which means they're going to be kind of heavy. If the watch you want to buy feels light as a feather, it's definitely not real. If you're not sure, take a trip to a Louis Vuitton boutique, hold a watch that that you know for sure is real and compare its weight to the weight of the watch you want to buy.
Pay attention to the monogram of the watch. Make sure it looks right. The monogram on authentic watches will always be symmetrical and will never be horizontal. The letters "LV" should also be totally visible and complete. If they're cut off, or if they're hidden behind any of the hardware of the watch you want to buy, you can be sure you've got a fake.
If you've already bought your watch and want to know for sure if it's real, take it to an appraiser. It's the best way to find out the real deal. They're trained to spot fakes, and can give you a 100-percent answer on whether you've got a fake or a real Louis Vuitton watch.