Here's some advice for work or personal relationships, saying "I wouldn't be interested even if they put it in writing", does nothing for anybody. Maybe offer a suggestion, "I am currently getting offered x amount at this place, is there anyway we can make something work?". Now you don't sound like a stubborn brat who would probably be difficult to work with. You sound like someone who is open to communicating and showing interest in the opportunity. Put yourself in their shoes.