I actually had this happen to me this week. I had a client/tenant staying in a property. They had kids. When it came time for us to do the move-out I was shocked on how perfect they had left the property. I notified my landlord who came to the property and her idea of "perfect" was far different than mine. She said that she saw tiny scratches on the floor where kids had played with toys. She brought a light out and showed me. I was a little shocked as even with my prescription glasses on I could barely see them. I explained to the landlord that the small scratches were ordinary wear and tear. She insisted that I call a hardwood floor specialist out to look at the property. She refused to return their security deposit. After a lot of back and forth I finally convinced her to give the entire security deposit back to the tenant. Sometimes it is easier for a property manager to mitigate the issue. If you need more information on HUD's guidelines please read tenants and landlord guidelines for security deposits.
Check out HUD's site for more information