Hello,
The only best practice really is to update the AdWords API with your new data as it changes in your system. This should be possible if the request is structured properly, so I want to focus on what's going wrong with the request if he's getting an error.
Can you provide more details on the specific error he's getting? You can only ADD an item that doesn't already exist; to update an existing item, you need to use the SET operation. Hopefully it's that simple, but if it's more complicated I will need more information to help out, such as what service you're using, and full SOAP request/response logs, to look into this further.
Regards,
Mike, AdWords API Team