When I bought my house my realtor convinced me to make a much lower offer than I had planned. Even after the negotiation was all done I still ended up paying less than I had been planning to offer initially. Cost them some commission, but I'll happily use them for any future transactions and recommend them to others needing a realtor.

Not all realtors are out to maximize the commission on a single transaction. Many are like lawyers and are working for the best interests of their client (which is also in their long term interest).