Just to add two things:
1) It's not a scam. If marketed correctly and disclosures are placed appropriately and the merchant generally follows FTC guidelines for these type of offers, it's a perfectly, valid business model. As mentioned, it's been around for decades, and some of the biggest companies built their business on negative option type offers. Also, a lot of the people signing up are aware of these charges. It's not like they are all completely blind and clueless, though that's definitely a big part of them. And neither is the content garbage/worthless. Sure, it can be, but there are plenty of good/decent offers out there, where customers are actually fine with paying one membership fee.
Where most companies fail however is with proper disclosures and providing support. And that's what in many cases gets them nailed by the FTC. As I mentioned earlier, quite a large number of people are aware of the trial period. But if you try and screw the customer with your terms, lie to them and tell them their account was canceled, when it wasn't, double or triple charge them and cross sell them to hell or have one support agent to handle 500 calls, then of course you are going rack up complaints like crazy. This has nothing to do with the business mode or offer though, as the OP tries to imply. A shady, thieving advertiser is going to be scamming people regardless, it's just that these offers make it easier and require less start up cost.
2) People are stupid, gullible, greedy, stupid, push overs, computer illiterates, liars and stupid. You have people calling in, stating they've been "scammed" before with a similar offer and asking the agent whether that's also the case with this site, only to yet again join the same type of offer. People simply don't learn. You have people deciding that instead of using "foo234" as the login that was sent to them, they would simply enter 234 instead, and upon discovering this doesn't work, call to complain that they've been scammed. People will call to cancel, only to go ahead a week later and charge back the amount, claiming it is an authorize transaction that the had no knowledge of. Customers will associate any similar offer they've seen at any point in their life with the product they eventual go with, only to call and complain that feature X is missing or the advertised price was not what they've been actually charged.
You will have customers join a site, cancel and complain about hidden fees, only to come back 2 days later to try and join the same site again, and upon discovering that they email is barred, call support and claim they've never seen the site before. And most of them are actually serious. There's customers that canceled too late and in turn got charged, that still receive at least a partial refund, for which they are really grateful initially. Once that feeling settled, they decide they could do better though, and charge back the whole amount, claiming again unauthorized use. And even if sites follow FTC guidelines to the T, there will still be morons with their credit card in hand, ready to disregard any text that's not bold, underlined and with a font size of at least 24px, typing in their personal information as if it's a contest. These are the same people that when confronted with the obviously placed terms, will come up with any excuse to cover up their moronic existence, usually by claiming the terms have been added after they joined.
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So what's the point of this, besides ranting a bit?
There have always been shady companies out to scam customers, and they are going to exist in the future as well. The internet just made it a lot easier for them.
And even if you follow every guideline, law and regulation on the book, you will still have people crying fraud and complaining to each other, because people are simple stupid and ignorant. And if someone truly believes they are joining earncashwithacaiberries.com, then the best support and the most compliant site in existence of the internet will not convince that moron that maybe he should just stick to collecting welfare instead.
Oh and apparently processing fee = shipping & handling = CD shipped by mail = virtual product only = scam.