So, I can sort of appreciate where you are coming from: if someone doesn't buy salt and instead keeps going to the fast food restaurant down the street grabbing handfuls of salt packets, they are being a pretty awful leech, as the reason salt packets are free and just available like that is because we trust people to not abuse the process like that. The alternative turns into what we have to do with packets of BBQ sauce, carefully limiting how many people are allowed for various food purchases, and then charging them $0.25 for extra.

I can also see an argument that this person has discovered a security exploit that they are taking advantage of, akin to someone stealing wifi from an airplane hotspot. Whether because the person figured out an SQL injection attack in the website or because they figure out they can tunnel TCP over DNS, the more ethical thing to do is probably to report the bug to the company instead of abusing it to steal resources.

This, however, is a different situation: AVIS seems to seriously be mis-pricing their core product, and in a way that is kind of sketchy to begin with. Here we have a company that is doing something I can't imagine many of us actually like: they have built a ludicrous time wasting procedure by which they abuse human psychology to encourage specific buying patterns, and they did it in a way that is well-known to be dumb. The way they have done this is by manipulating prices of products and providing an alternative currency with incentives for specific behaviors. If you want to see threads worth of people hating on this, search Hacker News for SkipLagged (the site that was sued for finding open jaw flight segments being priced incorrectly by airlines).

Let's say I go into a Walmart, and they have decided to offer a $40 off discount on jeans, but they sell a pair of one of their brands jeans for $30, and the register treats the $10 as a credit. I tell the person at the counter about this, and they tell me "yeah, it's dumb; I just work here". And then I go to the checkout with a massive pile of jeans, and the people at the register at first give me a funny look, but then a wave of realization hits them and they start laughing. And then every day I come in and they have a basket of jeans sitting at the counter waiting for me. And they just don't care. In fact, the way you should model this is "Walmart seriously believes the price of jeans to be -$10", not "we are stealing money from Walmart". Sure, we think they are daft for valuing jeans at -$10, but we even told the people there and no one cared. They helped us do this.

If you want a real world example, Sony sells Playstations at a loss. Some people would buy Playstations, install Linux on them, and then use them as nodes in Beowulf clusters, or as cheap fileservers for their house. Sony does this as an exploit against our buying behavior, making us more willing to put down the initial investment for the game console so we are more likely to buy games later. They then put a ton of DRM on their hardware, require companies who want to distribute software for their platform to pay them a royalty fee, and extract their rent from game developers.

I see why they do this, but I hate it. It means that their entire business model is built in a way that encourages them to do things like sue people who jailbreak their consoles, as their profit is now tied to their ability to get paid for people developing and distributing software. If you ever wonder why Apple is so benign against jailbreakers while Sony sues them to death, it is because Apple has a business model where they make all their money on hardware (the App Store pretty much breaks even), making them only care about what you do with your device after you pay for it due to a combination of a control fetish, a strong aversion to bad PR, and a feeling of responsibility to protect their beginner userbase.

But like, even barring these indirect effects, Sony has incorrectly priced something they have put on the market. They haven't done anything fundamentally different from someone willing to sell stock at a price higher than the market rate. When people here talk about arbitrage, it is because that is exactly what has happened: someone is pricing their product in a way that has encouraged someone to figure out how to extract value from it. Maybe you also hate high frequency traders, but it isn't quite fair to equate them to pick pockets and con artists. If we found out the people selling the stock were doing it at a loss, it makes them dumb, not the high-frequency traders evil.

So while I can't imagine spending time finding these pricing mistakes, much less making all these phone calls and doing all this traveling to take advantage of them, the idea that this guy did is something I am totally fine with: "more power to him", I say. The usual worst case scenario that could come out of this is the "that's why we can't have good things" result of "no more stupidly complex promotional programs" (a similar situation to "no more free BBQ sauce packets"), but again: that would be a good thing, so I am having a difficult time feeling like this was due to someone doing something bad for humanity.

(For my part, I run a marketplace, and I have a strict policy against illogical pricing promotions: I stare at every single discount a developer wants to have me apply to sales made via my platform, and I verify they don't have pricing paradoxes that would lead customers to have to waste their lives trying to figure out how to get the software they want at the cheapest possible price. And I really do consider doing anything else, as is all too typical in the travel industry, kind of scummy :/.)