I know this thread is super old, and hopefully you've had a better SL experience since posting this.....but I'm responding because this still came up at the top of the search results when I was looking for something and I think it might confuse/discourage a lot of people with similar questions. Hopefully this can help those people.
As someone who has both played gold hunt and who put coins on my land, the coins DO pay. Land owners/shop owners/etc. pre-pay them for them to even work and every time someone collected one, my balance that I paid to the coin definitely went down. If they exist to make land owners happy and scam other people, *I* certanily did not see those perks.
What you may not realize is that once you collect a coin (or several coins) you have to then go to the gold hunt land and collect your lindens from their ATM machine. They don't just go straight to your linden balance...you have to go collect. I used to go every time I'd get to 100L$, for example. Plus, if you start collecting before you "register" on the goldtokens website (that's the gold hunt version that I played, anyway), it might not count everything you collected. I ran into that when I first started, but after I "registered" I had no problems collecting every linden I earned AFTER registering. I did lose some of what I had collected prior to registering on the website. It probably has something to do with the system not keeping track of names of people who aren't "officially" playing or something. The instructions are all available right there when you click the coin.
And many of the coins are actually worth less than a linden, so you have to collect many of them to add them up and have any meaningful income. It's a time suck, for sure (which is why I no longer play). But for some people it is worth it. Some people make tens of thousands of lindens playing gold hunt....the website you log in to check your balance shows rankings and what people earn, so...you can see for yourself. It's up to you if it's the right way for you to get lindens.
So, the reason they "get away with it" is because the coins actually do pay and there's nothing for them to "get away with". It's your own fault if you don't follow the instructions and then go collect your earnings.
The people who SHOULD complain are the ones who put the coins on their land and have to pay a "tax" to the gold hunt people every time they add to their coin balance....just to have traffic on their land that doesn't care about anything except collecting coins. Yeah it's kind of a little nice to have the traffic boost, but I'd rather have people spending time paying attention to what I've put my work in to instead of just tramping around collecting fractions of lindens and then leaving. Like it's not my job to fund other people's Second Life. There is very little benefit in the gold hunt for most land owners because we just pour money into it and get nothing back except a slight traffic boost. And it kind of tackys-up your build to have a bunch of coins laying around.
My traffic with the gold hunt coins, for example, would be at least 98% people coming just to collect coins and then leave. Very few actually stayed to look around, and unless you put out the coins that pay higher amounts and require people to stay on the land at least 5 minutes, it doesn't even COUNT in your traffic statistics....so it's definitely a worse deal for the land owners than for the people who might be midly inconvenienced by playing.
"Traffic boosting" contraptions/games are rarely as beneficial as people want them to be....because you almost always get the people there who just want to be there to collect money and who have no interest in what is on your land.