...which means if Amazon wants to avoid criminal behavior, they could ban such objects and not hurt legit sellers.

But if Amaozt doesn't care, this system is not enough to convict a criminal.

OTOH my friend has spent the past 5 or so years earning high six figures hunting good deals from big retailers and reselling on Amazon.

I’m sure he’s only one of many. There’s nothing Amazon can do without banning such sellers.

Sometimes consumers sell something they decided not to use. Either directly to another consumer, or to an aggregator who can turn a profit on the consumer's loss by obtaining lots of previously retail bought goods.

It's sunk cost fallacy to just think "I must use this thing if I can only sell it at a loss."

You can make a small but moderate side income reselling clearance LEGO on eBay. Even with the Walmart sticker still on it, no theft involved.

Or international arbitrage. Lots of stuff sold cheaper in USA than other places. Even stuff like a big bottle of ibuprofen or allergy pills are much more expensive in Canada.

While arbitraging deodorant sounds silly, I have bought EU roll-on deodorants online before because they're not much of a thing in North America. And they don't melt into a mess in a hot car.

Deodorants are hardly a thing in SE Asia, partly because of biology/genetic differences: https://www.nytimes.com/2018/02/02/business/china-consumers-...

There can also be customs arbitrage as small packages from little sellers can slip through.

Usually because you avoid tax legitimate business pay (import tarrifs, vat)

Tax evasion may be profitable, so is shoplifting.

Scalping deodorant as a startup?

The trick is to get it on clearance. Some local stores will sell for a massive discount off amazon.

I do more ebay as I won't touch selling used on amazon but in the past I have bought pallets of new stuff at local auctions and sold them on amazon for significant profit. Ended up with several cases of Ember mugs once. Forget the price per mug but think I paid ~$600 and sold em for ~$2400 on amazon.