"Why do people have such a blind trust in these companies?" When speculators, investors, and various new numismatists become involved in buying and selling of coins, certified specimens are an attractive draw. Speculators and investors, particularly if they are new to the numismatic industry, generally see certified coins as selling well, along with being highly marketable because of the grade guarantee, and naturally purchase them. Additionally, ‘slabs’ are easier to sell, because the grade, for the most part, is set in stone, at least to a further extent then a uncertified ‘raw’ coin. New hobbyists, being inexperienced, see certified coins as being a safer buy, with far less risk of over-grading or faking. These people, along with other numismatists, have a blind trust in third-party grading companies because by almost everyone these companies are considered unbiased, as opposed to the seller or buyer and trustworthy simply because they have small benefit for being dishonest. Over time, it became more and more common for many to see the grade, see the company, and move right on to the price-haggling. For many, the name and the grade became all that were needed to make the click on "Purchase". For many, blindly trusting a third-party grading company became a natural thing. "Why do people have such a blind trust in these companies?" Because for many, the question, if any were asked, was, "Why not?"
"When should/do we employ them?" This one is fairly simple to answer. We employ them for protection of coins that are expensive either monetarily or sentimentally. That protection comes in the form of the strong, safe cases third-party grading companies place graded coins in, and from the certified, guaranteed grade. When investing in expensive coins, either buying ‘slabbed’ ones, or submitting them is another manner of employment of third-party grading companies. Authenticating rare varieties and errors is another use. These companies have multiple, good, beneficial ways to employ them.
People employ them for non-biased expert services. They dominate in an industry thanks to the trust and need in them people have created. Their general non-bias, industry dominance, and investment safety give them the blind-trust of many. The uses for them are numerous. They are third-party grading companies. An important factor in modern day numismatics, and a useful one too, I am not suggesting the elimination of them, or some sort of dramatic modification of them. I think they serve a great purpose, and certainly do not worsen numismatics. But I do say this; simply because they have importance does not mean they are the final word. We don’t need to have complete compliance, and shouldn’t. There may be reason to keep and employ them, but not to blindly trust them.