John notices that Mary's yard needs mowing and weed-eating so he goes over and does so. He sends Mary an invoice for $40 for his services. Can he expect her to pay him? What if they had been talking about mowing her yard and he is in the business of doing so. She seeshim in her yard with the landscaping design truck; he gets out and nods towards his mower and her yard and she smiles and nods at him. Can he expect payment now? What's the difference in the two scenarios?