One thing that often catches me out when I sell things is the Paypal fees. I always use Paypal goods and services so that both myself as the seller and the buyer are protected if something goes wrong. This means that I pay a fee. I try to include the fees in my price by guessing what they will cost and adding it to the price of the item but I usually lose money anyway because I underestimate them and also because I don’t want the buyer to have to pay too high a price.
This Paypal fee calculator is recommended by many people though, and in future I am definitely going to use it. Find it here
If someone you do not know asks you to pay via Paypal Friends and Family, do not do it. If something goes wrong you are not protected. Even if you do a trade/swap with someone you do not know and have not swapped with before, cover yourself by each paying an agreed sum to the other via Paypal Goods and Services. That way if one of the parcels is lost or the swap is not honoured, you can get the money.