It's a huge problem.
The only way to prevent it is to take your seatpin out every couple of months, regrease it with carbon paste and refit.
It is also CRUCIAL that you don't overtighten as this makes seizure even more likely.
If possible use a seatpost and frame where you know the size is very precise and not just an approximation. Put 27,2 seatpost that really measures 27,3 into a 27,2 frame that really measures 27,1 and you will see what I mean. This happens more regularly than you might think.