How to remove completely stuck saddle post from frame I am helping a friend fix his bike that he got for free. Everything went well, except that I cant raise the saddle. The seatpost is really stuck in the frame. 

The clamp was easily removed. When I tried to turn the saddle only the saddle itself is turning, and the seatpost remained stuck. I tightened the saddle bracket as hard as I could, and I managed to turn the seat post a few millimeters back and forth. But somehow it is even more stuck now and I can't move it at all. I am afraid that I will bend/break the bracket in the seat if I tighten it anymore. 

I tried with a pipe wrench and still couldn't twist it. Perhaps I will be able to if I have another person holding the bike so I have two hands for the wrench. I did manage to damage the surface of the seat post though. 

I have a few questions:


How would a professional remove the seatpost?
Why is it even stuck? Can this happen because of rust, or is it more likely because the previous owner hammered a 30.2mm seatpost into a frame meant for 30mm? I can see at the Wikipediaartikel (link) that both 29.6, 29.8, 30.0, 30.2 and 30.4mm are common sizes. As I don't have a precise caliper I can only tell you that it is approximately 30mm. 
If it is because of rust, can I polish off the rust and use the same seatpost again? If so, should I polish the post or the internal part of the frame?
Penetrating oil (Liquid Wrench).
It may take a few days as it needs to work its way down.
Or it may free it up in a few minutes.     

The risk you take with a lot of force with a pipe wrench is you bend the bike or brake off the post or get the post out of round.  

You should grease the seatpost to help prevent this.  If you don't bend the post then I would reuse it. 

It is most likely rust.  You cannot hammer in an over sized seatpost.  

If you do sacrifice the seatpost and use a use a lot of force with a pipe wrench then don't have the pipe wrench close to the bike as you could get the post out of round and really jam it in there.  That may have happened when you got it to move a bit and then jammed.

You have a couple comments of use heat and I don't disagree but I would hit it with penetrating oil for a couple days before I resorted to heat.  Not just once.  You need to hit every few hours with oil.  If you do go heat then heat gun before torch.