Assalmu alaikum,
I use Ebay, but I have had a very bad experience there (a scam) few months back. It was with an expensive and sought after item I was selling.
After the scam, I discovered under the fecade of reliablity and security advertised everywhere, PayPal are actually very unreliable when it comes to protecting you. I have now stopped using them and will not go back ever.
If you wish to continue using PayPal, I would recommend you do not leave any lump some of money in there, withdraw it into your account as soon as possible, as soon as a large some of money comes in. Dont leave it in there as they could 'freeze it' indeffinately and then take it off you with some reason.
Do not despatch a really expensive item to unconfirmed addresses, rather to confirmed address, if you want use PayPal, .
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Keep a receipt of postage if possible, in case the buyer claims they have not received it.
Make sure you are charging sufficient for postage and packaging. Know roughly how much certain weighs will cost to send. Remember you have to package the item too and take it over to the post office, so charge enough postage money to cover all these costs, as you dont want to eat into the money you made for the item itself as this could mean you make no profit selling the item or even lose out.
Thats all I can think of for the time being. Generally, the cheaper the item, the safer the transaction.