Try to be as confident as you can without coming across as cocky. You obviously know about bodywork, so you ought to be able to answer technical questions in an informed way.
When they ask you if you have any questions, don't do in with "how much bonus can I earn, and how many holidays do I get?" Ask them about the type of work you'd have to do, their preferred methods of doing the job, what products they use etc. Make them think that you can fit into their way of doing things, even if you don't agree with them.