If this is a standard software client, such as Sage 100 with no major third party enhancements, then I have been successfully recommending Gold Plans, since Sage should be able to work on these types of issues. I sell them on Gold Plans based on access to Anytime Learning and discounts on additional users and standard modules, and then mention unlimited support, but I don't lead with the support aspect. We also have a detailed document providing guidelines on when the client should call Sage and when they should call us.
We have a number of clients on service agreements with defined levels of service, but they are all identical in relation to errors and file issues. Many of these are JobOps users, where file issues are more complex, so support under a Gold Plan is many times not applicable. Our philosophy on file issues is to take preventive actions, so major issues are minimized. To this end, the common element of our agreements is file and log review on a weekly basis. We fix issues found and point out errors that start occurring in order to identify something which may have changed - new user, new procedure, hardware changes - so that element may be changed to avoid the error.
We also are proactive regarding network, infrastructure and workstation status, since we have a network support group. Even when we are not the primary network support vendor, we review and make recommendations on what we see as potential network issues that could cause software issues. This includes confirmation that backups are valid. Although this is included in our service agreements, it many times has resulted in taking over all network support with a separate agreement.
There are going to be cases where something catastrophic occurs that was unpredictable. This is where having a valid backup is key. I have no problem telling a client to restore, because downtime is minimized and the integrity of data may be more certain. Also I hope we have the type of relationship where if they or their network support group caused this, they will take responsibility and pay for it. Otherwise, yes, you just suck it up and fix the issue. You can't have exceptions to this type of service agreement, unless they are specifically defined, as in the above examples.