Your Book Ground Rules
First, the confession. Depending upon the book, I may dog-ear pages, write in the margins, underline, put stars next to particularly important parts, scrawl a point of disagreement with the author, put question marks next to points that are unclear, etc.
Ultra-expensive books rarely get such treatment. Non-fiction is more likely to be scrawled upon because I see it as a tool. A cheap paperback novel might get dog-eared but I use index cards as bookmarks in most instances.
There may be some bias. A copy of War and Peace will receive reverential treatment. A paperback mystery or western may not.
Do you have ground rules for the treatment of your books?