Idont think there is anything wrong with a regular septic tank. Anyone that used to live in the country has had a septic tank, my parents have had one forever and the concrete ones work for a long time. It wont hurt to ask though.
The comps should be based on what other homes with septics are selling for in that area, so it shouldn’t be a problem unless there’s an issue with it. I’d get a septic inspection to make sure since they’re about 15-18k in our area.