I LOVED being in merchentainment!! Hated it in real life, but seriously, Disney is so not real life. It was amazing. I don't even really remember 'selling' stuff, I just remember all the good times. I personally think merchandise is one of the best roles to have because you get to really talk to the guests more than most roles. I loved the guest interactions. You get to meet people from all over the world, and that is awesome. Take advantage of that. Take interest in your guests and where they are from, because they will all be happy you asked, and really, I really was interested. I met so many people from so many different countries.
Beyond that, you can have so much fun with merchandise. I used to put on a crown and grab a wand every day and act like a princess. Who doesn't want to be a princess everyday? The great part about that, you wouldn't believe the number of kids that asked for my autograph. I'm kinda famous

And if it wasn't the princess get-up, I'd wear an apron and chefs hat, or Mickey gloves (sometimes all at the same time), and sometimes I'd grab a bear and pretend we were having adoptions and only the perfect little boy or girl could go home with that bear.
So much fun, best role out there. You'll love it if you remember to have fun with it. I worked at Main Street East in Magic Kingdom in WDW, time of my life!