The worst thing a real estate agent can do is negotiate their own worth via the commission they are potentially going to earn. You would want a real estate professional, one working on the behalf of the buyer, to go in with the knowledge of the transaction process, the knowledge of the market value of the home, and make certain you get the best deal. Period. The seller then pays the commission to all brokers (agents) involved. If an agent starts to discount their commission while acting as a buyer's agent just to get the deal done, they are probably not closing a great deal of business and put little value on their time, effort and experience. In today's market, it costs a great deal of money to be successful, and ultinately, as in anything in life, you get what you pay for.
I work for an independant Broker in Dublin Ohio. The reason an agent can offer such a large rebate varies. If they work for a brokerage that doesn't charge the agent a large split of the commission, the agent controls more of the commission and can offer a rebate to attract buyers. Other agents are depending on a spouses income and do real estate more as a hobby than to make a living, so they can offer rebates. Others may offer a rebate as a business model to earn less for each buyer and get more business by using this attractive rebate. If you have a realtor you trust, that is worth alot!
Good luck on the home purchase!
Here's a great article about chosing a real estate agent to help you.
Hope this helps. Good luck to you and happy house hunting.
Elliot Lau, Realtor of 22 years