Yes John, it is perfect logic to relate low feedback rate with low success rate. But in my position I have to be careful not to leap into conclusions without taking envidence. I am very careful, maybe too careful sometimes, too careful to mention any particular agency names and make comments even of that I've worked for before.
The reason is here, I know the service quality of some agencies but I don't know the average standard of this trade so I can't make the judgment whether those ones I know are below or above average, in other words, bad or good.
The chnlove success story link is indeed some kind of ads but the credibility is acceptable. I believe at least they are all real cases. From your comparison of their data with that of brother's stories here, I feel you are inclined to place more trust in the later. This reminds me of an example I once read in an economic book, that people are usually more influenced by comments of a product from one friend or neighbour than from one hundred strangers. This is not rational but indeed human.
To make clear my attitude here. (It might be bias from my own experience) I am not going to believe there are any good or bad agencies unless chnlove take some substantial measures to improve service quality of all agencies. So far, I only believe there are agencies who sometimes do good things a little more than bad things.
More than effort, luck is still what you will rely on in adventures on chnlove especially at the beginning.