Are fungal toxins a significant problem in coffee, and if so, can they be avoided?
Time to apply a bit of healthy skepticism here:

The blog post:


Is (so far) the first and only one I've ever seen stating mold to be a practical problem in coffee - in the sense of being present in a high enough quantity to matter (mold grows everywhere).
Uses all kinds of weasel words to describe symptoms ("edgy", "cranky", "useless mentally").
Describes symptoms that are well in line with plain old caffeine withdrawal.
Frequently links to other blog posts on the same site, most of which are "top 10 ways" and "top 5 reasons" fluff pieces.
Manages to cite and thoroughly misuse two studies: one from 1995, and another from 2003. Both are about Ochratoxin A (OA), which isn't even the biggest risk; Aflatoxin is. (More on these later).
Advertises a fairly expensive product, sold by the same author.


The author:


Is, according to his LinkedIn profile (which I refuse to link here), the VP of Cloud Security at Trend Micro - a Silicon Valley tech company. I could not find any evidence that he or his his employer has any experience in human biology or nutrition.
Makes all sorts of unusual claims about himself: "He upgraded his brain by >20 IQ points, lowered his biological age, and lost 100 lbs without using calories or exercise."
Has an entire page of testimonials, which he frequently cites as "evidence".
Has an entire site dedicated to product-peddling, including the ubiquitous six-second abs (yes, that's hyperbole) and a $60 "earthing mat".
Has the following disclaimers on the product site (all in tiny print at the bottom):


  The statements made on this website have not been evaluated by the FDA (U.S. Food &amp; Drug Administration).  Our products are not intended to diagnose, treat, cure, or prevent any disease.
  
  The information provided by this website or this company is not a substitute for a face-to-face consultation with your physician, and should not be construed as individual medical advice.  The testimonials on this website are individual cases and do not guarantee that you will get the same results.
  In short, he employs tactics which are commonplace among con artists selling magnetic bracelets. In my opinion, all his claims are technobabble, and I think they are not trustworthy. 
  
  The facts and studies:



The largest sample tested was just 60 samples of beans, and was tested from only one source (Brazil). This is fine for individual studies, but in the real world there are hundreds (thousands?) of sources from many different countries. It's safe to say that the current studies don't even come close to testing all of the coffee from around the world.
Both OA studies found an incidence rate of approximately 50% for the OA-producing mold, at wildly different concentrations (minimum 0.2 ppb in one study, maximum 7.8 ppb in another). If this tells me anything at all, it's that you should probably vary your source if you want to minimize your risk.
Neither the FDA nor the EFSA actually have a legal limit for OA, but the EFSA "suggests" a limit of 8 µg/kg, which means that even the worst samples are below the very conservative legal limit.
One study actually tested the incidence of OA in brewed coffee, not just the beans, and found a maximum of 7.8 ppb in the brew (that's 7.8 µg per 1 kg of ground coffee).

For reference, there's an EFSA directive recommending an intake of no more than 120 ng/kg (body weight) per week, which comes out to 8.4 µg/week for a 150 lb/70 kg individual, or 1.2 µg/day.
Based on the worst contamination of brewed coffee (7.8 µg/kg), doing the math, you'd have to consume the brew from 150 g of ground coffee per day. That's about half a standard-sized tin of coffee. Per day. If you drink that much coffee, shame on you.

The 3rd study (the one rumtscho linked to, not cited by the blogger/con artist) looked at Aflatoxin, not Ochratoxin, which actually is regulated by the FDA at a maximum of 20 ppb. This study also showed approximately a 50% incidence rate after roasting, with the highest concentration of AT being 16 µg/kg for decaf (less with caffeine). So that means with any random cup of coffee you have up to a 50% chance of consuming an amount of AT that's still well below the FDA limit - that's very nearly zero risk.
None of the studies test the rate of mold growth on beans while in storage under various conditions (temperature, humidity, etc.), so we can't comment on what happens in storage. So I guess if you want to really be on the safe side, only buy as much coffee as you think you can use in a week or two.


Conclusion:

Don't believe everything that people tell you - especially people with something to sell. Unless you're drinking gallons of coffee a day, brewed coffee is perfectly safe.