Yes, it's very common. It's rarely a good idea to talk to just one service provider before committing and estate agents are no different.
As ClubMan says, some may suggest an unrealistically high value in order to convince you to choose them so you need to be wary of that. I'd suggest going to viewings of properties close to your own to get a sense of how the agents perform in real viewings. I did that when selling my last place and I was able to rule out one company I was considering as the agent really didn't impress.