The problem with an agent taking responsibility for this type of information is that it can change. If on Tuesday they tell you, and thus take responsibility for the accuracy for the information that there are no registered sex offenders in the neighborhood and on Wednesday one arrives, the agent didn't do anything wrong but you are still going to be ticked off. This information is generally available through state or county websites like the one I've posted below and I encourage my clients to do their own research by checking such sites and actually meeting neighbors prior to being fully contractually committed.
One other consideration, these sites can only tell you where the "registered" sex offenders are supposed to be. Often times, the unregistered and mobile ones are just as big of a risk. There is also the risk one moves in next door the day after closing. There is only so much you can do.
Here's the thing, Home Owner. Real estate agents have a different responsibility than you think. One is to practice within the constraints of our license. That means to be responsible in everything we do.
When we go outside of that domain - to provide legal advice, construction advice, research land-use information or do research on police records - we then take on the role of "expert," and are responsible for the accuracy of that information. We are not experts in locating Registered Sex Offenders, who, by the way, are not a Protected Class under the Fair Housing Act. (They have other rights to privacy, but that's another matter.)
So if we were to, say, search a site like McGruff, and find out that an RSO lived across the street, and told you what we found . . . and didn't discover the one living next door to him, you might feel justified in faulting us for not doing thorough enough research - we acted like an expert, and didn't perform to that level.
As for ethics, Realtors(r) subscribe to a formal Code of Ethics, which anybody can look at and know what to expect from us. Researching RSOs is not part of our duty to the public.
All the best,