You shouldn't be, at least not in such cases. I guess it's primarily due to your inexperience with Bitcointalk, i.e. wannabe genuine posters can fool you. Similarly, it is more likely that someone who is completely incompetent, yet is offering *management* services, could fool you into thinking that they know what they're doing.
When looking for a manager for signature or bounty campaigns, you don't need to look far. Starting with this very section, you can see atriz, and Harlot tend to bump their threads often. There are some other activate/proven managers, e.g. Lutpin, yahoo62278, edward, and me. Contact a few of them and try to come to an agreement. Watch out for people who tend to *low-ball* (i.e. ask a very low amount in payment) and people who sweet talk their deal/services/etc., as those are usually the most incompetent ones.