I know im really late here, but fuck it, whoever reads this is lucky. Not sure if this counts as a life hack but whatever. I used to do this as a kid, and honestly, it was absolutely GENIUS. I used to make like 2,000 dollars a week as a 13 year old. I honestly never wanted to tell anyone this because I was scared they would do it and ruin it for me by overdoing it/fucking it up and getting caught.. I'm going to go into detail here, so sorry for the long read. Here's the scam:

This scam works best with a partner in crime. First you go into a dept store, and find an item that is out on the shelves, relatively unnoticeable (something you can carry and it not be too heavy or large) but something relatively valuable (300-700$) . Purchase this item. Go back into the store and find your friend who has picked out the same item as you and something really small and cheap they want to purchase. This next part is incredibly important! Though you probably don't have to go through all this, this is what we did. I would walk to an area that was far away from the register where my friend was waiting with the exact item I purchased. We would do somewhat of a nonchalant switch where I put down the one that I purchased and picked up the EXACT ITEM they had in their hand,(the one that I did not purchase). I know it sounds confusing, so read this slowly and try to follow me here. My friend, would then take the one I purchased, and walk away. I would take the duplicate of the item I chose (the one I didn't purchase, that my friend was holding) and leave the store with it. Honestly, the alarm almost never went off. But the few times it did, it was no problem, I had a receipt for the item and the guard would never question me further after showing it. I would leave the store and put the item in a safe place (usually my car or somewhere far away from the store in a hidden spot). MY friend would go back to the shelf and hide the item that I actually purchased DEEP into the back of the shelf and mark it, so we knew which one it was. He would then purchase the small item, just so it didn't seem suspicious that he was there for no reason, and leave the store. I would come back the next day with a bunch of bags and items from a different store (like toilet rolls from wall mart) (my friend would walk in the same time as me). I'd then hand the bag in my hand to my friend, walk back to the spot where my friend hid the item that I purchased the day before, take it to check out, and return the item for a full refund. I would then walk out of the store, where my friend would follow me shortly after. There are a lot of variations of what to do with the bags, how to renter the store, how to leave, so that was just one way I did it. My friend and I did this for about 3 years, and we lived like kings as teens, haha. Let's just say, I had all the best baseball bats, baseball gloves, gameconsoles, computer games, computer monitors, anything you can think of.