Hi Antonio,
This is completely a very normal situation and SAP Standard where for the one time customer you need to change the details every time you use, and that is the reason we call them one time customer.
if you really wanted the customer with fixed address and details in that case you should have opted for the account group other than one time.
What I can suggest is first make up you mind and get cleared with your business if they want the one time customer or regular customer for the quotation.
if it is one time customer in that case you need to enter the address and all the required details.
if in case you dont want this detals to me be mandatory you can make the required changes in the account group - field status, where in those details can be suppressed.
I hope this should be helpful
Kind Regards,
Sridhar.