I am a Realtor in VA. My colleague @Russell Brazil is correct. In VA an agent does need to document who they are representing in a transaction and do so in writing. I also agree with my friend @Jeff Copeland that if you want a great agent, you will need to sign an agreement. But there are ways around this.
Know there are many real estate brokerage models out there. Some companies send out an agent who is available to show you the home. Today it is Jim and tomorrow it is Sally. That works for some. But most investors want someone they can cansult with on an ongoing basis. They want someone they can trust and someone to develop a relationship with. If that is you let me explain how I handle it and give you some ideas on how to proceed.
First if you are a wholesaler, I will pass. I have yet to find how a wholesaler and an experienced agent can work together in a mutually beneficial way.
If you are a buy and hold investor, I will pretty much insist you sign an exclusive buyer agency agreement. It is likely your deal will come off the MLS and we all have the same info, I don't want to find you went off and worked exclusively with the listing agent or some other agent showed you the home and wrote the contract. However, I have no problem limiting our agreement to MLS properties so if someone presents you with an off market deal, you can decide how to proceed.
If you are a flipper, I will encourage you to not sign an all encompassing buyer agency. In our market, most likely your deal will not be a MLS deal but off market. I will have you sign something that states if I show you the home you work with me. I expect and understand that you will be searching far and wide for a great deal. No one agent can know all off market deals.
In fact sometimes with off market deals, I tell the investor to contact the seller directly without me with the understanding that if they get it, they will list it with me on the back end. If you violate that hanshake agreement, goodbye. I have yet to have someone go behind my back on that. Sure you may find an off market buyer in the end but you had better remember me or that is our last conversation.
Bottom line, requirements for agency agreements are dictated by state law but there is no requirement in any state I am aware of that the agreement be exclusive in all situations. Exclusive to a home shown yes but every investor must be free to work any and all options in an optimal way
Hope that helps.