how do i remove shipping charge from a product?

We have products that can be purchased and shipped and we also sell classes (at a physical location) and other services which do not require a shipping charge. We made the classes and services another product and we have standard shipping rates ($5.40) that get added.

as a workaround I added -5.40 to the “Extra Shipping Cost” field which actually does subtract the shipping from the total.

The problem now is that when some people go to paypal they get an error.

“There was a problem connecting to PayPal to setup your purchase. Please try again.

10427 – Invalid Data – Shipping total is invalid.”

My question is what is the proper way to deal with different products that do not need to be shipped and therefor do not require a shipping cost.

Thank you.