What a bunch of ******** advice.

1) Put down the hammer
2) Ream out the seat tube and clean. Drill + soft brush reamer = key
3) Make triple sure that is the seatpost size the frame is supposed to take, it's not unusual for some idiot to have slammed in a post that was too big to begin with.
4) You can also go down one size in seatpost and see if that is the correct size. If it's too small DO NOT USE it.

PUT THE HAMMER DOWN