Hello and welcome! :wavey:
You're smart to avoid Ebay yourself, but you're right when you say other people won't realize and get a bunch of scrappers, which they might unknowingly pass onto you. All you can do is inspect the pin before you trade and use your best judgment. If it has rough edges, strange colors, paint dips etc, beware! Especially hidden mickey pins. Also, if you're dealing with another kid, check out the other pins on their lanyard. Where there's one scrapper, there's many, if they bought a lot on Ebay. Some fakes are hard to catch, but if you see other clear fakes on someone's lanyard, beware!
You can check pin pics and see which pins have scrapper warnings, they'll be towards the bottom of the pin's page if there is one.
For cast members, your best bet to avoid scrappers is trading with cast members that are sort of off to the side and not as public, therefore not as traded with, such as small store workers or custodial workers. Also, try to get cast members as they come out of "employee only" areas, chances are they're just starting their shift with a refreshed lanyard! Another way to catch cast members just starting their shift is first thing in the morning - the parks just opened and they haven't traded much yet, so the chances of them having scrappers are lower.
Also, beware of pin boards and pin books/bags which are available at certain locations under different circumstances - they can be a whole lot of fun because there's so many pins to choose from, but they can turn up a lot of scrappers!
Okay, that's about all I can think of lol. Best of luck on your trip, hope you and your son get awesome, real pins!