The sort of questions to consider when committing to provide support and maintenance are:

Does the support and maintenance agreement actually reflect the process of the support team?
If not, you risk either being liable for breach of contract or, more typically, providing support that you are not contractually obliged to provide and therefore missing the opportunity to charge additional costs.

Have you distinguished between maintenance releases and releases containing new functionality?
Unless your budgets include the distribution of new functionality at no extra cost, contracts should provide for the ability to charge existing customers for new functionality.

What contractual commitments have you made to response/fix times?
Despite the fact that you may use your best efforts to meet these times, you should avoid contractual liabilities if you fail to meet response/fix times.

Have you adequately ring-fenced the software that you are supporting?
You should not be committed to fixing faults that are not due directly to your software, whether they are as a result of third party or legacy software, or other reasons.