First off I just want to say that threads like this shouldn't be made. If you're going to quit then quit making a thread documenting all your failure is just going to discourage others. Second, just about every method you listed is proven. My theory is this you likely have a major defect in your technique and instead of trying to correct whatever the defect is you move on to a new method.
I think on the contrary that these are good lessons for many of us
In particular, it shows that 90% of what is being taught by the gurus does not work for the humble mortal.
There is an old saying that gurus start offering their methods only when they are about to be obsolete. There is certainly some truth there.
It seems that the web is switching to more and more personal connection: you use the web to get contacts and future buyers, not to sell directly. People really buy YOUR services/knowledge/know how... and not the crappy products that every body else sells. You start selling when you have a real contact with people. Also, that's the best way to understand exactly what the market wants. Sure, this is not a generality, but I am convinced it will be more and more like that.
In your attempts, you haven't tried amazon type products. At least, these are not crappy products and you are backed up by a first class sales organization. You seem to be proficient in SEO, and that should be sufficient to get consistent sales.
An other hint: if you can really get top 3 ranking for 'dentist in xyz', you are sitting on a fortune... You might perhaps hire a phoning company to make appointments and be able to close the sale in person. You might also want to better target your future clients (typically, you should target those who are currently investing on the web such as adwords and are not successful at SEO). You are however unlikely to succeed if you simply send a dozen emails.
Hope these will help to recover your moral