What impresses higgens about eliza's offer of a shilling for her lessons?What impresses higgens about eliza's offer of a shilling for her lessons?

He is impressed because a shilling would be considered a fortune to Eliza.

HIGGINS [walking up and down the room, rattling his keys and his cash in his pockets] You know, Pickering, if you consider a shilling, not as a simple shilling, but as a percentage of this girl’s income, it works out as fully equivalent to sixty

or seventy guineas from a millionaire.