I like the points made in The Really Bad News About Bad Customers.
Very wise. Only trouble is I could go and find an equally interesting story about a small business following its nose that turned into a great success. With hindsight, its relatively easy to see whether a customer is worth it or not, and to see which rule from the Business 101 rulebook could be used to prove you right or wrong. And many of the ‘rules’ are essentially just opinions. The levels of fact and experience that underpin them are highly variable.
In small business, its important to be focussed on the 20% of things that deliver 80% of the benefits. But at the same time, you need to be open to the left-field opportunity. Right or wrong, someone will no doubt point out (with hindsight) how it should have been obvious.
But it rarely is obvious at the time. In small business, it helps to have a good plan, listen to good advice, and then make a good decision. And to be lucky.