We sometimes buy feminized seed ourselves, and there are still a high percentage of males. This is a result of a weak STS process and/or lack of due diligence (best practices) of the seed producer to catch and pull any pre-flower hermafradites. There are three ways of feminizing. First, STS is the most common way, and the most reliable method. Second, Collided Silver Spray which is less used, as it is harder on the plant and has been known to have a higher non-feminized rate. Third, Manual Magnification (under a magnifying glass) looking for dimples and volcanos, this method has the highest inaccuracy of all.
We here at Las Vegas Greens ALWAYS utilize two of the above methods for every crop we grow. We use our own STS spray and Manual Magnification. We meticulously examine every plant throughout the grow on a daily basis. Our feedback from growers who have used our seed has been exceptionally positive, as our seed lives up to all supporting State and Independent Lab test results.