It's worth $20,000, you pay $10,000, are you happy?

Seller wanted a quick sale, buyer wanted a great deal.

I believe that’s called win-win!

I agree with others who say that as long as it was the seller’s asking price, it is not unethical. As SnakesCatLady said, I would tell the seller that she could probably get more for it from another buyer. If she said anything along the lines of I just want to get rid of it, I wouldn’t feel bad.

If, however, someone knowingly low-balled a grieving widow, that is IMHO, total douchebaggery.

I agree - that’s what I’d do.