Most agents are happy to show one of their listings regardless you have an agent or not. In the rare situation where an agent tells you that you need to be represented to tour a home, you can ask if those are the wishes of the seller. A seller would have to explicitly instruct their agent to not show their home to self-represented buyers.
Some agents would feel more comfortable being there to host a showing for self-represented buyers which you can offer up as an option.
If the agent continues to refuse to allow you to see the home, you can reach out to their brokerage and ask if this agent is acting in a way that represents the brokerage.
Of course, people selling their homes would welcome your request. It is just one of the ways it is more streamlined to work directly with the seller.
For more answers about how to work with a selling agent as a self-represented buyer, check out our Home Buyer's Guide!