Or you could read the terms of the business relationship with PayPal:

  Am I allowed to presell?
  Yes, you are allowed to presell items as long as you follow these guidelines.
  Off eBay presale requirements
  If you sell items in an online store (not eBay), you must guarantee delivery 
  within 20 days from the date of purchase and make sure that the customer     
  knows they are buying a presale item.
  [...]
  If you are selling goods or services in an online store (not eBay), you may 
  be allowed to presell items but we may hold your money in a reserve 
  account or limit what you can do with your account to reduce the higher risks 
  associated with presale items.

Or as the ruder ones of us said in the 90s on Usenet: RTFM.

https://www.paypal-businesscenter.com/content/presale-policy...