What is normal wear and tear? I have a property manager who looked under the rug to see if she saw ...?

She looked under the rug to see if she saw anything,is that normally how u look for damges to a carpet. Because the upside looks perfectly fine. Its been shampood and it was because of urine stains on it from a pet and spilled drinks. There is no evidence whatsoever of damages on top,BUT ther is underneath,im just wondering can i be charged for somethjing underneath the rug?!! lol. And she also wants to take.well did take pics of it ,and took pics of the furnace which is full of soot because they didn't change the filter in 30 days as written in the lease. Can she charge me with something they failed to do every 30 days? I have never in my LIFE been in a situation like this,seems as though she is nit-picking,even though shes not gonna get a raise for charging me any extra for this because she is not a private landlord,but a property manager of a aprtment complex!!lol Plz help someone who is experienced w/ things like this!! Thanks.