We often have customers complaining that our applications run significantly slower after they receive an upgrade. Our usual procedure is always telling them tha

We often have customers complaining that our applications run significantly slower after they receive an upgrade. Our usual procedure is always telling them that we have not seen any performance regression internally or at other customers, so we kindly ask them to look over what other changes they have made to their environment, be it hardware or software.' If they insist that the problem is our software, we tell them that we will begin troubleshooting, but if the error is outside of our responsibility, we will bill for all the hours used. 19 out of 20 times we restore the old version and benchmark them against each other and the performance is comparable. At that point they go back and recheck something, and it turns out they allocated resources differently or another application was upgraded too.