Maybe it's different in your neck of the woods, but around here, it's standard for buyers to sign a contract with their buying agent which restricts them from working with any other agents for 6 months.
I would have said something similar not long ago but I have an agent helping me look right now, and I haven't signed anything. My first day starting to look, I went to about 5 open houses on a Sunday afternoon on my own. I chatted very briefly with the realtors at each one, but didn't say very much. They all want you to sign in though, so I put my name and email address.
One emailed me with some similar houses I might be interested in. It was about two weeks later when I responded to see if she would show me some others that I had seen on MLS. We've now gone out about 4 times to look at places, and she never asked me to sign anything. I will be buying in a few weeks, and I will use her to do the deal (I like her and I'd feel guilty otherwise anyway) but I did think it was odd that she never asked me to sign anything before we looked at houses the first time.