At my studio we frequently have people bring in things to fire. Our rules are that they either need to know what cone their piece fires at or know the company/person/manufacturer that made it. SO many people get stuff at garage sales and thrift shops and have no clue. Or they get clay but can’t remember when or where and they don’t have the box anymore. If they don’t know we tell them we can try to fire it but if it doesn’t work we can’t refund their money, and if it damages the kiln shelf they have to pay to replace it [65 dollars]. To me this seems reasonable. We don’t want to damage our supplies OR someone’s piece. But people can’t understand and we often have disappointed/upset customers. Does this happen in your studio? What are your rules on firing?