If the seller does not have an agent, then you can probably save time, headache, and money by asking an agent to represent you. In many states, the agent has standard purchasing contracts and relationships with attorneys, title companies, etc. which can get you discounted fees and have one "central" person taking care of all the tasks involved. Also, even with for sale by owners, the sellers are almost always willing to pay the buyer's agent fee.
However, if the home is on the MLS the commission has already been set aside for the buyer's agent. I often hear the argument that the buyer will negotiate that away from the listing agent. This will rarely happen.
First, the listing contract is in writing so the seller is obligated to pay the entire commission regardless of what you offer. Second, if the listing agent (who has an existing relationship with the seller) is going to give anyone a discount on his commission, it will likely be the seller. Third, the listing agent will earn that commission becuase they will need to do the work that the buyer's agent normally would.
At the end of the day hiring a buyer's agent that you trust is free but it appears that you would prefer not to work with one so you will end up working the listing agent of the house you like. My guess is that next time you will hire your own buyer's agent but I have been wrong before. I hope that helps.