[Zeke]

"They are looking for big ticket items." Sure that's what a thief would do, buy a diamond ring and steal a candy bar.

They go through a short training to identify thieves' behavior traits. You might have a ham between your legs but they won't ask about it unless they don't see in on the list.
They might have been alerted by the floor walkers about a specific item, therefore the list check. It's a good way to start a detention.

For the most part it's all smoke and mirrors. Amateur thieves see the check and are intimidated. The pros enjoy it.

I have to pile on and say what's the big deal? You can legally walk through denying producing the receipt and they need probable cause for any further action. Continued likewise behavior will for sure attract more attention each time you enter.

Maybe that's what you're looking for.