I had Attractions, Merch, and Photopass as my top and I honestly don't think that they asked me any questions related to merch even though that's where they put me. I assme they could ask how you'd handle someone stealing, an upset guest, how you are working with money, basically anything in that realm.
As for pros and cons, I had never worked a retail job in my life and I LOVED it. Merchandise gets pins to trade which is probably the best thing about it. Merch is relatively easy and depending on where you get put, you have a ton of stores to work at, it's also really easy to pick up shifts somewhere else. I really enjoyed stock shifts because those give you a break from the guests and you're just backstage picking out things from a list and putting them on shelves. Merch doesn't change much from one location to another except stocking areas so it's not too difficult. You can talk to people a lot longer than Attractions or some other roles, depending on how many things they buy or how busy the store is. I ran into the same kid pin trading two days in a row and I met with an older gentleman and had a nice conversation with him and saw him later that week
Cons: I worked a lot of carts and it was so hot out, which will be hard. Magic bands can be really annoying and hard to explain to people or hard to get to work. Sometimes guests will speak different languages so you have to really pay attention to understand what they want if you're by yourself. ALWAYS carry your guide with info on where other merch and food is, and that lists times for shows. I forgot mine one day and was blasted by an older gentlemen who wanted the nearest hot dog and had forgotten to pick up a sheet that day to put in my pocket (even though I directed him to the restaurant next door to ask). Some locations are going to be better than others. I worked in Hollywood which was really easy to navigate and drive to and I worked anywhere from Muppets, to the Christmas Store, to the Prop Shop beside Lights, Motor's, Action as well as Indiana Jones and Tatooine Traders. You could get placed in areas that hardly move too such as a hotel or Mousegears at Epcot (which I believe only works there). People will often give you exact change or a few coins after you've opened the register so you'll have to manually calculate that and since I'm horrible at math it was a nightmare.
Overall it's an easy and fun job, I loved it.
ETA: You should also consider you might get put in a food area as well. I worked writer's stop so we had to make coffee and serve cookies and other snacks. You can get put in Big Top where you make slushies or the Confectionary where you have to make candy dipped apples and the lot. Writer's Stop was crazy and pretty difficult since I'd never really worked with coffee either and it got so busy during the holidays.
