It happened to me before, claiming the listing will not prevent it. I claimed all my listings, and one of my listings was "transferred" to another agent who is miles away from my market. I mean the listing was taken over by another agent, I couldn't do anything with it at all. It would redirect the viewer to that agent's website everytime you clicked the link. I ended up sent an email to Trulia, they fixed it and it did not happen any more.
It is true, anyone can claim any listings on this web site, no one will know unless the listing agent keeps checking their listings.