could be Salt Monger - I'm sure of the Monger part , I'd be happier to find Sand ( from the Severn Estuary ) or Stone ( from the Forest) as the items he was selling :-)

looking again its more like Sell Monger, which I think is an archaic form of Merchant. < Thanks M for the off line suggestion of Fell Monger>

then he becomes a Haulier (1851) later in life