The short answer is: Trulia (and Zillow) exist to shimmy in between consumers and Realtors and be the middle man. That's how they make money, and that's why they exist. They didn't create their sites with cute toys and graphics solely for the consumer's enjoyment. They market heavily to Realtors, and have to give (a little) return on investment. A Realtor should be able to give you a value, though, and those services are not commission based. If you're relying on the values that these sites are giving you to make any sort of decision, I wouldn't. They're not "real".