Wow! I'm sure they're really confused now. I'd go with the residential agent - ask exactly what experience they've had - just the same style home isn't enough to be experienced.
What if this agent has NEVER done a property on well and septic before and the home you want is on well and septic? Those two are monsters right there if an an agent's never done it. I know I read an article where an agent sold a couple a house that was on well and septic...and the couple wanted to build an in-ground swimming pool on the nice, flat cleared area right behind their house...and they discovered AFTER closing that is where the drainfield is! Agent got sued. How in heavens name could that have EVER happened?