Let me clarify my questions and make them more detailed:

2. Can we use our customers' accounts?

Your answer: "Regarding your second question, the shipping manager automatically fills in the shipping labels with customer address information from your Point of Sale Receipt or Sales Order forms."

That is an answer to a different question. Our customers have their own UPS accounts and their own UPS account numbers. They give us their UPS account number. We use their UPS account number and the shipping charge gets charged to their account. We put their UPS account number in the shipping manager. Can I put their UPS account into the new QB manager so that our customer will get the charge from UPS?

3. Can we use OUR negotiated rates and not ShipEngine's rates?

Your answer: " the shipping cost is determined by the package destination, shipping options, weight, and selected service. Therefore, negotiated rates are not available."

I don't think you understand my question. All shipping costs are always determined by those things. We put that information into the QB system. The QB system sends that information to the shipping company (like UPS). UPS looks at that information and calculates the cost according to the account that is being used. When I connected my UPS account to the ShipEngine setup, does that mean that ShipEngine is going to send UPS all the information including my own UPS account number so that charge is the charge of my negotiated rates with UPS? Are we going to be forced to take the shipping rates that are charged by ShipStation?