Identifying your ideal customers
The traditional demographics of size, sector and location are hopelessly inadequate when trying to determine whether any given organisation has the potential to turn into a good customer. Structural, behavioural, environmental and situational factors are all far more important predictors of success.
This sort of intelligence cannot be gathered through "buying in a list". It requires a clear sense of the characteristics you are looking for, and the commitment to conduct your own research. But without a consensus about what an ideal customer looks like, companies inevitably waste a huge amount of energy pursuing the wrong prospects.