CardsFan
Thinks s/he gets paid by the post
I spoke with a contact (who mentored DD) at a high-quality engineering/geology firm nearby. He's going to have an engineer take a look at the lot and give us a verbal opinion for about $500.
Good start. But will he have access to the property? In any event, he can give you a professional opinion of the possibility of building on it. Unless he finds a glaring reason, expect an opinion of something like 75%/25%, one way or the other.
But it is doubtful he can give you a definitive answer on septic without a perk test and a complete inspection of the property.