Software development contract – how many free support hours to give client?

I'm writing a contract template for my new software dev business, and it includes a 30-day warranty period, which is industry-standard according to my research, that we would, essentially fix bugs for free to ensure it operate up to spec. My question is, how do I structure the cost for the time that my team need to spend answering the support tickets? After 30 days, I can bill the client normal hours, but can I do the same during the warranty period? Basically, we would lose money if the client call me everyday about issues that turn out to be just user error, and my team have to spend time explaining it to them, which wouldn't be covered under warranty since it's not our fault. We can bill them these hours but I'm worried that doing this may damage our relationship with the client. Another approach to this would be to give x number of free support hours, but I don't know how to come up with this number. Any experienced insights would be much appreciated.