In Ch.18 Jaggers announces that Pip has 'great expectations' and that he has to go to London to become a gentleman. In Ch.19 Pip decides to buy himself a new suit of clothes and visits Mr. Trabb the tailor. Trabb is having his breakfast and initially doesn't consider Pip to be a prospective customer, but the moment Pip casually displays hard cash to him Trabb becomes very deferential and even addresses him as 'sir' :
`I am going up to my guardian in London,' said I, casually drawing some guineas out of my pocket and looking at them; `and I want a fashionable suit of clothes to go in. I wish to pay for them,' I added -- otherwise I thought he might only pretend to make them -- `with ready money.'
`My dear sir,' said Mr Trabb, as he respectfully bent his body, opened his arms, and took the liberty of touching me on the out- side of each elbow, `don't hurt me by mentioning that.
A little later, Trabb's shop assistant a very cheeky boy - "Mr Trabb's boy was the most audacious boy in all that country side" - who would always insult Pip is scolded by Trabb; and it is then that Pip is fully satisfied in knowing the power of money:
"my [Pip] first decided experience of the stupendous power of money, was, that it had morally laid upon his back, Trabb's boy."