Facebook is expanding its custom audiences tools to let advertisers target based on information from third party sites like Datalogix, Epsilon, Acxiom, and BlueKai. This means a car company, for example, could target users on Facebook that have been ID-ed by third parties as being in the market to buy a new car. While privacy advocates will likely sound the emergency alarm, it’s an opportunity for big brands to increase efficiency and spend money on users likely to return the favor.