>>Absolutely! Even if you pad the heck out of your quote, you'll likely lose in the end due to all the things the customer hasn't told you or decides to change during the course of the project.
>>
>>That is called a change request and is not within the scope of the original spec. Change requests should be implemented on a time and materials basis only.
>
>You may call it a change request. The customer may call it an assumption.

The original scope agreement should include a list of assumptions. If it's not on the list, it's not an assumption.