A "targeted spammer" (usually just "spammer") is an account created to spam Fluther. The spamming is carried out by specifically targeting threads with certian topics.
Signs of a targeted spammer:
Answers are less obviously spam (compared to mass spammers) and often include links. They sometimes contain price information.
Not all answers are the exact same, but all contain similar links and content, usually related to the topic of the thread.
Answers a lot of questions on a specific topic. They typically do not generate a very large number of spammy answers.
Username is either related to the product (freecash4u), complete jibberish (yu57dfsgs), or an actual name (WilliamSmith).
Targeted spammers are not as easily detected as mass spammers. While mass spammers might generate a large number of flags, targeted spammers might only get flagged by an observant member. Since the answers are on-topic, it takes a more detailed investigation to reveal that the user is spamming a large number of similar threads with similar answers. These spammers also tend to spam older questions.