Here is a checklist from PayPal's FAQ regarding Chargebacks. Follow each step on the list, substituting the address portion for online information I'd assume, and you should be fine. If you're dealing with any blackhat material ONLY accept bitcoin. Use paypal for things that are legal and you can explain to paypal staff why you were selling it.
- Describe the item that you are selling in as much detail as possible and as accurately as possible. Include pictures, measurements (if applicable), and other relevant specifics.
- Make every effort to know your customer and to respond promptly to any customer service requests.
- Keep as much information as you can about the transaction and your customer, including email or other correspondence.
- Publish your return policy in your auction listings or on your website. Also include your return policy in email correspondence with your customer. Please note that certain laws and credit card issuer policies provide that buyers may have chargeback rights for merchandise that is not delivered or is defective, even if your policy indicates that all sales are final and that you do not allow returns.
- Ship to the buyer's address listed on the Transaction Details page and retain proof of delivery that can be tracked online.