i have several books that have NO spine creases....but i have others that were passed down to me that have many spine creases.   i am wondering whether i should post them here or just send them to the thrift store. 

how do YOU determine if a book has too many spine creases? (assuming spine is fine and no other damage but you can see like 10 creases or whatever). 

Spine creases are a natural part of book aging. As long as the spine is still intact inside, creases are not a factor to me, unless they are so many that the spine is starting to become loose. I certainly wouldn't ever COUNT the creases, that's just petty. If it's solid, its good. IMO.

I agree. This is a used book site, so I expect spine creases on paperbacks. I usually read paperbacks and cause no creases or few, but I do not expect that everyone else is as anal as I am.

I also agree!!! spine creases happen..and I'd post them as long as the spine creases aren't so bad that they are causing the pages to fall out. 

Yeah Thomas...I try and not crease the spine but, it happens.

spine creases happen, it's when they are so severe that the pages begin to seperate from the spine, there in lies your problem.  Creasing, ok.  Seperation, not ok.