OK so I asked PP about this, here is the answer-Sadly, it is possible for a vendor to take repeated charges from your paypal account. I learned that the hard way when I used paypal to pay for something, and the following month I got dinged again for the same amount. I discovered that Paypal was allowing it, and I had to remove that vendor from authorized payees in my paypal account (in essence I had to blacklist them). I disputed the charge and got my money back.
So no vendor can make subsequent charges without authorization unless you have signed up for any sort of subscribed payments, like maybe automatic renewal of forum membership....if you make a one time payment without agreeing to any subscription then you will not be charged without authorization.
However, please do read for any terms with merchant's website if they are processing any subscription for automatic payment. If there is no such terms and condition then the payment will be a one time transaction.