Don't you ever wonder

I have seen a couple of episodes where the boss had a real problem employee, who had no sob story...but was just a poor employee with a bad attitude. For example Boston Market and Hooters. Both instances had bad employees and managers that were eventually fired or sent for more training.

But yes, I know what you mean. You don't see many employees on these shows who come from stable and comfortable backgrounds who are just there for more spending money for Xbox games or because they don't get enough allowance. It's always someone who is supporting a family of 10 on that paycheck, has a special needs child, had to abandon their dreams of medical school to support an ailing parent or family member, is a recovering drug addict/criminal trying to work their way back to a normal life, etc...

I have worked in retail myself, but most of the employees were college kids working for extra spending money, had a higher earning spouse, etc..

How the bosses always manage to find the people with the best sob stories? I would say that it was up to the people behind the scenes, but then the workers would have to go through some sort of a screening/interview process and they would definitely know what's up and that ruins the premise of the show.

Maybe the boss meets up with 20 employees and the 15 that are boring are never aired and the 5 with good stories are aired.

It's fiction.
There is no such thing as "reality TV". If you read the small print during the credits, it even states some scenes shot for entertainment purposes.
It's still a TV show and it's made to entertain, so some situations are "manufactured" for entertainment.
Even more so, they would not even be allowed to film unless they tell people whatever they are filming for. Even the "fake documentary" thing does not hold water. It's called "full disclosure", they HAVE to tell the people they are filming what they are filming. So everyone is fully aware they are on Undercover Boss even if part of the "magic" is telling the audience they do not know, when in reality they do know.

If they actually made an honest "reality" TV show, it would be boring as hell.

And so, God came forth and proclaimed widescreen is the best.
Sony 16:9

It astonishes me that people still don't understand how these shows work.

The employees that are filmed in the episodes are cast by a casting department. They are interviewed about their jobs and their personal lives. This is how they find hard working people who have touching stories (or slackers who need to be exposed).

As they say SEVERAL TIMES in the duration of the show, the employees think this is a DIFFERENT reality show. They are told throughout the whole process that it's some bogus reality show where the "contestant" they'll be training has a chance to win money to start their own business. This is literally said in every. Single. Episode.

How else do you think they're able to mic, interview, and film the employees during the show? It's not hidden cameras. The employees are perfectly aware that a reality show is being filmed. They're just told it's something else.

You may be sitting there thinking, "Wow, they're so stupid, how do they not know it's Undercover Boss?" There's a lot that goes on behind the scenes that you don't see. So don't judge until you're sitting in that seat yourself.

This show is so, so, SOOO set up!! Of course they screen these people and already know every single story that is going to be told.

Everybody who lives long enough will have a story of lay-offs or serious illness or so on.

They change the story every few seasons of the "Reality Show" part of the show.

In the first 2 or 3 seasons it was "people looking 4 a new job because they lost there job do 2 the Great Recession" show.

Now it's "person looking 2 start there own business" show.

I'm sure they'll change the "reality" part of the show again 2 hide the bosses soon.