In general credit card providers will assume that you are doing your job of managing stock before you offer the goods for sale.
Nevertheless, if goods have to be ordered in, or go out of stock in fast moving environments, or need to be customised, then it is legitimate for orders to be placed for goods that won't be shipped immediately.
In many countries best practise (sometimes even required though not followed by all merchants) is to charge for the goods when they are shipped. Authorising a transaction for collection later is the normal way of doing this. It implicitly confirms that the transaction would have gone through, and puts a hold on the customer's funds until you are ready to "capture" them.
These holds roll off fairly quickly (typically in a range of 14 - 30 days) after which a new transaction would be needed. If a transaction isn't needed it can usually be cancelled or voided before then (check with Paypal about the specifics of their service in your region).
There is an alternative approach that just checks the legitimacy of the card by passing a small transaction that often doesn't actually hit the customer's card anyway. But I'd be surprised if Paypal offer that. That's more likely to be used by a large retailer who has the infrastructure to store card details and go back to pass a fresh transaction when they are ready to ship, and of course has the drawback that there's no guarantee that the funds will actually be there.