Good luck bernie - don't go in thinking "it's only a part time job" - you have got a lot further than many other people with no interviews at all.! You could say that you hope that the part time hours they are offering at the moment might lead to something more if they find you reliable and trustworthy, and that you are interested in working in retail (if you are). If you know the sort of shoppers you get in the store (eg younger, older, mixed) if you can show that a bit of the understanding of their likely needs, that might help. Good luck - let us know how you get on.