Job interview at Pestmart - how nice should I dress?

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I pretty much have the job already but this is the first interview. I am applying to be a pet trainer. Normally, I go on office job interviews and wear clacks and a button shirt or a business suit. Should I go that far out for this type of job or would a nice pair of jeans a button down shirt (or dressy shirt) do? My interview in a bout 2 hours and I am starting to worry about it because I have never had a retail job interview before (other than B&N who also wants to hire me and i just wore a t-shirt and wide legged pants and my tennis shoes) I was thinking about going to Old Navy and picking up a nice new top to wear with jeans or my wide leg pants. Should I or should I not wear heels?