I am not a TX licensed agent, and therefore cannot address the laws of agency which apply in your state. I would recommend that you gain a thorough understanding of the agency relationships that apply in your state, as it may have a substantial impact. Ms. Summers replies earlier that, absent a buyer agency agreement, the agent will be representing the seller. As a buyer, that would be unfavorable to you. As Ms. Summers suggests, you can draft buyer agency agreements for brief periods, even a day. Once you become acquatinted and confident with an agent, you can draft your agreement for a longer period of time. BTW, Tman in is neither a licensed agent, nor is he a resident of Texas, and he has a history of mulitple facutally inaccurate posts, so do consider thses facts before heeding any advice from him.
As a general statement, agents will work harder for the buyers with whom they have contractual agreements. Your best advice will come from those RE Pros in Texas, since agency relationships and the laws governing them vary state to state. There are many general questions on Trulia which can be answered equally well by persons from outside of the state of the question. In your case, I recommend that you place prioroty on the answers that come from RE Pros within Texas.
Best of luck