The intent and outline of the brief article is sound enough. It's just that his English is unclear. Depending on spell checkers is no help for errors of context or simply saying the opposite of what is meant. A copy reader would probably pick up the errors and a kindly reader would ignore them. A sloppy reader, unfortunately, would assume the writer means what the text states. And that would be unfortunate.
From the context the author appears to be an English native speaker. If he's not, then I would not like to be harsh, though even then the text should go past a sense checker.
Examples:
"When I began learning about the trading using technical analysis over 20-years ago I filtered through much of the same information you are."
"Before we do that, if you have not read the article I wrote called Bringing Common Sense to Trading. In it you will learn how to trade prices action that has moved too far too fast."
"In the above chart of Google (GOOG), once prices began their move higher there weren't any pullbacks of significance. While conventional thinking would suggest that prices would or should pullback it didn't happen. You see, overbought is a flawed concept that does work and it will limit what you believe is possible."
By sloppy writing, the intent is lost. Omitting a "not" is no help on the road to enlightenment.
And just as an aside, the "overbought" and "oversold" indicators are not usually assumed to be trustworthy on their own, needing confirmation. A stock can be oversold achingly long and overbought seemingly forever. The slopes of hope stretch to infinity and the wall of worry has no limits...our cash and patience do.