When travelling to and from Toba/Samosir beware of Pt. bagus Taxi's. They scammed two separate people we saw into buying multiple seats for themselves. When we told them what we paid they were both fuming, but the conman (Jule is his name) pretty much told them they were idiots and to just get in the car.
They will also tell you you must prebook days in advance the taxi's from them which isn't true.
There are multiple taxi companies there and the prices are negotiable, dont use Pt Bagus