Actually that is my secret, use only your fingers. If it won't open with just your fingers, it is too snug and will probably crack if you use a tool of any sort. By using your fingers, it may hurt, but after awhile, just like with playing a guitar, your fingers will develop calluses.
I have had lots of practice. I can build a house out of plastic if I had saved them all.
Do you keep the good ones ? I'm sure you could probably sell them. However, after this thread, maybe it's not the right thing to do.
I throw everything out.
Do the slabs go in the recycle bin?
I try, but most of the time they take them out not knowing what they are.