our position is this.
If the client requires a press pass they are informed the following before the job enters production:
The job has been estimated with XX minutes makeready, and xxx Sheets makeready allowance. We print to ISO standard and the allowances enable us to print to the standard. If during the press pass, the client decides to move away from this standard and consequently exceeds these allowances, then the additional time/sheets are chargeable.
This tends to work as a rule, after all, if the files are created and prepped, and the proof is accurate i.e. all your processes are calibrated. Then there should only be minor variation from what the client has seen.
... and then sales get involved!!