I've bought and sold on there for years never yet had any issues. If you're asking them to post items pay with paypal and pay the fees just like you do on here then you have protection if anything goes wrong.
You are just making a private sale
Most people are honest, but its the scrotes that make things go bad
Protect the money you send and gather as much information as you can (their name & address, but the dodgy ones will lie if they can)
I have bought 3 markers off of people on preloaded and never had any issues and i have sold a couple on there as well always ask for it to be sent with tracking and always ask for name address and a phone number and give the number a ring to confirm that it is a correct number and pay with PayPal and don't use friends and family option
Ps good luck