But it is easy to fall into the hands of the Philistines.
The fundamental reason why it is so hard to form any just opinion of detectives in general is that (except by their fruits) there is little opportunity to discriminate between the able and the incapable.

Now, the more difficult and complicated his task the less likely is the sleuth (honest or otherwise) to succeed.

The chances are a good deal more than even that he will never solve the mystery for which he is engaged.
Thus at the end of three months you will have only his reports and his bill--which are poor comfort, to say the least.

And yet he may have really worked eighteen hours a day in your service.

But a dishonest detective has only to disappear (and take his ease for the same period) and send you his reports and his bill--and you will have only his word for how much work he has done and how much money he has spent.