I need some way to let my customers buy and pay directly at the product without "putting" it in the cart. I want my customers to buy only one product at a time. And I really don't need the shipping method selection either.. When the customer sees the product he or she shall click on a "buy" button (not an "add to cart" button) and be redirected directly to the payment/checkout page.. And if they leave the page without paying, I don't want the product to stay "unpaid" waiting for them to pay.. If they leave the page everything shall be restored and normal again.
This will require a bit of customisation. An order would still need to be created in a background operation so that the payment and order details can be recorded Does the customer receive anything for the purchase - I assume as you don't need a shipping address it is not something physical - maybe a digital download or something ? What payment merchant / type are you going to use Paypal or other ?