This was also really common with TVs during the Super Bowl. People would come in and buy the biggest TV they could get, have their Super Bowl party and then return the TV.
It's more the depreciation and how quickly electronics evolve. People were using the returns as a free lifetime of upgrades.
One particularly stark example when I worked there a long time ago was someone who wanted to upgrade their old projection TV.
So four years after they bought it they brought it in and returned it. They got about $4k back. They walked out on the floor, picked up a brand new LCD TV for $2k and almost half a decade after their original purchase they walked out with a brand new, upgraded TV and $2k in their pocket.
You can imagine how this can be abused with most electronics that Costco sells. Imagine going in and getting a brand new upgraded laptop every 2-3 years for the rest of your life after a single couple thousand dollar purchase.
I saw someone return a flat of steaks with half a remaining cooked steak left just saying "my guests thought they weren't very good".
Someone had a custom photo book printed and when they came to pick it up decided they didn't want it anymore and just got a refund.
Someone returned a plasma TV because of the glare from their windows.
My wife bought a car seat there (something you can't return _anywhere_) which we ended up not being able to get installed in the car (had the shitty cheap version of the LATCH clips that are impossible to get tightened up). Took it back for a full refund.
We bought a vacuum there that broke literally a week after the manufacturer's warranty. Brought it in and exchanged it for a new one.
There's no time limit on any of this.
This is by no means normal in North America. It's one of those Costco things like providing part time retail workers reasonable salaries and health benefits, etc that sounds insane in theory but obviously works for them.
I know personally there's been a couple times where I've been on the fence about buying something and ended up purchasing it because "If it sucks/falls apart in 6 months/whatever I can just bring it back."