same apt, different brokers, different rents

I am apartment hunting, and ended up contacting two different agents at different brokerages about the same apartment. I wasn't aware it was the same place -- they were advertised at different prices (a $150 difference in monthly rent!). I saw the apartment with the first broker, didn't sign anything. Only realized it was the same place when I showed up for my second appointment... and the broker had me sign a disclosure that he had shown me the apartment. I like the apartment, and would like to go with the broker whose disclosure I signed (the rent is $150 cheaper). How can it even happen that brokers are advertising the same apartment at different rent? And what is the right/legal thing to do if I decide to apply for the apartment?