John Lennon treated wealth and grandeur with derision. We find this attitude expressed in many of his songs.
When he writes, "Her baby buys her things you know, he buys her diamond rings you know, she says so", he's telling us that, "money CAN by me love", of a sort; but it isn't the real thing. The repetition of, "she said so", drives home the fact that his 'baby' loves him only for his money and the things which he buys for her with it: "you know";-)
John poked fun at all the materialistic things that he grew up without - and that suddenly came his way when the Beatles became the best known faces in the world. Remember that the Beatles (after a few cold starts) became fabulously wealthy, 'overnight', but John always stayed true to his roots and he never let us forget it.
A man of genuine high principal, with abundant satire always on his lips, he was taken from us, sadly, at a time when he had finally found some real happiness and direction in his life.
Rip John.