I just ordered a few magnets from their site, including one that can lift 100 kg. (http://www.supermagnete.de/eng/FTN-63) and worried about the exact same thing.

There's a shipping guide on their site, and apparently it's not as problematic as you would think since you can "shortcircuit" a magnet by wrapping a piece of metal around it. The guide is here: http://www.supermagnete.de/eng/faq/shipping