A random Youtube video got me surfing the world of b-stock liquidations and customer-return pallet picking.
For a moment, I almost got excited enough to buy a guide, then I realized WTF was I thinking. The only ones REALLY making money off this are the middlemen.
TL;DR: most companies don't mess with verifying returns. They toss them all in a pile, and periodically put them into pallets and dispose of them to liquidators. Liquidators then sell them to other liquidators, and they eventually end up being bought and sorted by some entrepreneurs and end up back on eBay or even Amazon.
If you can get a couple pallets of the stuff, and you have a warehouse, and the time to sort it and relist them on eBay, it can almost be a worthwhile investment to do it full-time, but you'll have a ton of garbage to dump periodically (typically 30% of items are broken or unsellable) and a lot of the stuff are just crap (that's why they are returned), and others are just too esoteric. And if you buy "processed loads" (i.e. someone already sorted through the stuff into categories) it's likely they already took the valuable items and left you the crappy stuff. On the other hand, unprocessed loads are worth more, obviously.
After looking at some of the prices for pallets, it's basically the wild wild west. A pallet can be as low as, say, $100 to 200 (the guy in the video bought 7 pallets and shipping across the country for 950) and he thinks he'll more than triple his money after sorting and listing the profitable items on eBay. On the other hand, some sites are listing the pallets for THOUSANDS, and supposedly "unprocessed" Walmart pallets can go for over 10000!!!!. It just seems so... tedious. You can buy a lot of 30-40 used laptops for like, 2000-4000, but who knows their condition after you got them. I guess you can clean them and resell them for $100 each... Maybe you'll get a gem worth $1000 purely by luck... and so on.
I guess if you like picking through stuff for the thrill of discovery it can be interesting.