How do you jump from one type of job to another?

I’ve been looking for jobs and just found one that I think would be an ideal next step. In my last job I was a food service manager; this job opening is a customer service rep position with one of our vendors.

Here’s why I want it: these guys sold us our coffee, and I love coffee and hopefully get bonus points for being familiar with their product. I’ve always wanted to go into something related to gourmet food/ drink, but store management was wearing me out. It’s a 9–5 position which would allow me to go back to school. The pay is a bit better and it’s a much shorter commute. It’s a local company, and I dig the idea of working somewhere that’s part of the community.

I think I can get in touch with the sales representative who worked with my store. He often visited us for training and to introduce new promotions or to fix the coffee equipment. If I use him as an introduction or a reference, how do I word that in my cover letter? I think this job is mostly administrative/ sales; what kind of questions should I prepare for if I get an interview? Any other advice?

Thanks a bunch, in advance.