Don't worry the Sainsbury's interview is very easy. They only ask you 5 or 6 basic questions like describe a time you received good customer service, why do you want to work for us, describe a time you worked in a team (mention something you did at school or something) etc you can find the questions using google. I had no experience too and interview was very easy I got the job. There's no role play (not in mine there wasn't at least) just a few simple questions that you prepare for beforehand. They won't ask you about lack of experience.