carpet

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My sister has a house in Cerritos, California.  The carpet was 10 years old and ok condition.  She rented it out to a family and for some reason, they were unable to move in so they subleased it to another person who owned a "tennis clinic."  From my understanding, it seemed like they were rooming several kids.  When when moved out, the carpet downstairs was full of ink stains.  The carpet cleaner looked at it and said he could not clean it.  My question is, how much of a deposit do we return to the tenants since it was not a brand new carpet.  Do we return a percentage of the cost of carpet?  If we replace with laminate, do we still replace a portion of the deposit?