Based on what I read, there are 2 options to go from Berlin to Szczecin, with train or shared ride. The train costs around 30 euro if booked online, while shared ride is only around 7 euro. I have some questions regarding this:

I am wondering if it will be cheaper to buy the train ticket on spot?

Is there another better option to go to Szczecin, for example by public bus?

Does any of you have experience taking a shared ride (from blablacar.com), is it comfortable?