1) Player Count
I like 3-5 people. It’s a common mistake to think that the more people you bring, the better you will do. Most rooms aren’t designed with huge numbers in mind. Bringing large numbers will leave players sitting around in rooms with a linear design. 3-5 players is a comfortable number that offers multiple points of view without leaving anyone out.
2) Double Check the Work
It happens all the time that a box or safe isn’t searched properly. Or sometimes, you put in the right code to a lock and it doesn’t work! Swap the person out. Maybe they’re tired and they’re hitting the wrong buttons. Or maybe they had a brain fart, and they’re not lining the numbers properly on locks.
I’m lucky enough to play with the same group of friends. We aren’t offended when we check each other’s work, but I wouldn’t recommend it if your group has people touchy about this sort of stuff.
Announce when you find something!