Can you provide a little more information? Was this something regarding an item, or a service? Did you get scammed of something besides money? If you pay someone for a [legitimate] service or item through paypal, and the person did not deliver the service/item promised, you can contact paypal, or your bank, or your credit card company (depends on what you used to pay) to file a claim and request a refund. Make sure to provide supporting documents like receipts. If it's something illegitimate, you might be out of luck--for example, purchasing neopoints using actual cash is not something paypal endorses, and if you get scammed, paypal is not liable to refund you. If you had disclosed any information to your scammer (account name, e-mail address, password), then change your password & the password of anything you do on the internet that might be similar to what you disclosed. Watch your account for a few months for unusual activities.
if you paid someone 100$ for something here than you were breaking the forums rules in the first place you can't trade until you're at least level 1
You charge back, or open a scamming case on where ever you bought it from. Or you take the loss (I'm down $120) or you find that ass and kill him