Lead quality is determined by an advertiser’s expectation, therefore it is crucial for an advertiser to communicate metrics to measure performance at the beginning of a campaign. A high quality lead will be more likely to convert to this metric as compared to a low quality lead. For example a lead sent into a call centre with an incorrect phone number will be low quality but if the same lead has a valid email address and is used in an email marketing campaign then priced appropriately it may be a high quality lead.
There are many different metrics that go towards determining whether a lead is high quality, including the source of the lead, the interest levels expressed when it was collected, the exclusivity of the data, whether the lead is 'hot' and verification of information.
Fundamentally the lead has to be gathered in the right way from the right place and then it has to be properly managed in order to generate a good return on investment.