Sell it for 399,999.00 you save approx $2800 between buyer and seller. I don’t think the other facts will change your tax situation much.
From a financial perspective you are prolly worse off with the $412,000 offer if you are using a real estate agent.
The real estate agent will take 6%(whatever % you agreed to) off $412,000 instead of $400,000.
6% of $12,000 is $720
There may also be other costs associated with selling it at a higher gross cost(each county is different).
I can understand why the seller would want to buy it for $412,000 with the $12,000 seller credit. He will likely require less down payment at closing.
From a tax perspective - everything else should be the same.