There are various ways people can send money through paypal to you. Some ways take longer for the funds to get in your account, some get posted immediately. You can sign in to your paypal account and see if a transaction is "pending" or "complete". You can also see your paypal balance. If the amount shows in your balance, and transaction shows "complete, you're safe to ship the item. Keep in mind that Paypal keeps a small portion of this transaction for a fee, I THINK it's like 2.9%. There's a lot more info on their site, but that's pretty much the basics.