If a neighbor re-graded the property that causes run-off to flow to your property, you may have a suit for nuisance and may seek injunctive relief.
If the shade violates a city building code, file a complaint with the local code enforcement officer.
I am not a CA attorney, laws vary from state to state, therefore you should always consult a local attorney.
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Mr. Millar gave you good advice. I would add that the letter you sent to the broker will have to be disclosed to the new buyer. Your best and cheapest bet is with the complaint to the City. As for the water issue, I would say that you sue both the new and old owner and let them hash it out. But I suspect that the issue will probably get resolved before having to do that, because the new buyer may force the seller to fix it.
I will caution you however, to make sure that your claims are well supported, since the seller could sue you for interfering with their sale.