Here is a simple hack that took me a while to locate, so here is a post to document…
The PayPal cart and buy now buttons allow you great variety in shipping, but how do you charge a flat rate for shipping per order? It isn’t obvious.
Add the following line of code to your “buy now” or “add to cart” button forms:
<input name="handling_cart" type="hidden" value="2.00" />
The value above is the flat rate you want to charge per cart in dollars.
The above works as long as people are ordering one type of product. If more than one product is added to the cart, the handling_cart value for that product will be added also. If someone knows how to get true per-order flat rate shipping implemented, let me know.