Here’s a Quora answer about how those claw arcade games work. You know the ones, you’ve probably won once, but just once. My inclination was to call this a ‘fascinating Quora answer,’ but upon thinking about it, it’s not fascinating. The machines work exactly how you think they would. The operators can vary the strength of the claw to screw you just bad enough you keep sliding in your dollar bills.
Basically, most crane games are designed so the claw is randomly (and only once in many games) strong enough to let players win. Some even weaken in strength after a short time so players get close to victory only to see it slip from their grasp! Since the manuals for many skill games are available online, this is not hard to verify.
The answerer then goes on to link to many manuals so you can see for yourself. (via @sunilnagaraj)