I found that realtors can't even do basic searches to determine which ISPs serve the house. To expect them to be aware of multiple GIS layers is likely way out

I found that realtors can't even do basic searches to determine which ISPs serve the house. To expect them to be aware of multiple GIS layers is likely way out of their normal scope. Maybe it shouldn't be? But thats how things are now. You, the client, should also do your own data collection from public and semi-public sources for things that are strictly outside MLS data capture.