Working with brokers

[Bryan H.]

When looking for an apartment I often hear to build relationships with brokers. If there is nothing currently on the market, and they know I'm looking to buy they may bring me a pocket listing etc etc. 

What if a broker has a listing I am interested in purchasing? As a 1st timer, is it best to get another broker to guide me? Or should I go straight to the listing broker to negotiate the deal? 

Should I put my trust in a residential agent for guidance? Or must it be a commercial broker?