Triaging - Do you remember that any changes you request will impact on budget and time?
Often towards the end of a project, you may request extra pieces of functionality ("Can you add a second email address field into the Client Contact form?"), or maybe another report is required. Even in the middle of a project extra work can be requested as project goals move. So long as there isn't a technical or business problem with the request, the work will be scheduled by the developers and done.
Every new item that is requested increases the total hours and scope of the project and therefore the cost. If the project has a drop-dead date or budget, don't ask for things that will blow these deadlines out. Or, if you want your developers to work to a budget, ask them to let you know what 'can't be done.'
Insist your software consultants correctly triage additional item requests.