To talk someone/something down can mean
A) to talk louder than someone
Example sentence:
- I wish that guy would stop talking everyone down. It would be nice to be able to have a conversation over dinner.
B) to talk to someone to calm them down
Example sentence:
- This guy at the market square must have been high on something. The police came, talked him down and took him to the station.
C) to help someone land an aircraft
Example sentence:
- My fight school instructor passed out in the middle of my first flying lesson. I had to be talked down by another instructor on the ground.
D) to persuade a seller to lower the price
Example sentence:
- When I was buying lunch at the market today, the fish monger had some grilled fish for sale. What he asked for it was too much but I managed to talk him down to a more reasonable price.
E) to make people thing less of something
Example sentence:
- The people of Lahti always talk their own hometown down. I don't get why. There is so much good to it.