How does Dickens use the characters and events in Great Expectations to show that wealth is corrupting?
This is an excellent question, and there are certainly plenty of aspects you could look at: the reality of Pip's London life, the description of his lodgings, the relationship that he has with Jaggers and precisely what activities he engages in with his wealth. However, I suggest that you focus on how the corrupting influence of wealth is suggested and foreshadowed even before Pip leaves the marshes. One crucial part of the text that you will want to focus on is at the end of Chapter 18, which is Pip's first night in his home with Joe and Biddy after finding out about his great expectations. Note how he describes his feelings:
...I drew away from the window, and sat down in my one chair by the bedside, feeling it very sorrowful and strange that this first night of my bright fortunes should be the loneliest I had ever known....
I put my light out, and crept into bed; and it was an uneasy bed now, and I never slept the old sound sleep in it any more.
Note how even before Pip arrives in London, the unease that he feels isolates him, making him feel lonely and separates him from those who love him best. Also spot the contrast between the "bright fortunes" and Pip's feelings of loss. The ease and comfort that Pip felt in his home is now lost. Also richly suggestive is the deliberate allusion at the end of Chapter 19, which is also the end of Book I of this novel:
And the mists had all solemnly risen now, and the world lay spread before me.
This is an allusion to Paradise Lost, when Satan arrives on earth and sees it spread before him. Such an allusion included at this critical stage in the novel, foreshadows the corrupting influence of wealth on Pip and in general.