World notes is one of my favourite things to collect. I love going to Foreign exchanges in airports or their offices in some of the cities I've visited.
I like UNC notes but to be honest I also love XF notes too because you can handle them and not worry about them being dropped or mis-handled when you show non collectors.
I usually have a list of current notes I am looking for, as well as a list of all of the offbeat places like Aruba or Macau, just in case. I always tell them I'm a collector,
and looking to spend about $100 or $50, so they know I'm going to make it worth their time to go through stuff for me. 90% of the time its a good experience, but if they
aren't interested in helping out a collector they will let you know and I just thank them for the time and walk away.
Make a list, and have it ready when you go out looking, you never know what you will find when you tell them you are interested in anything unusual or offbeat.