Other landlords have different policies, but personally, what I return depends on if things are damaged not caused by wear and tear. So that depends on how long a tenant rents from my place.

Eg., If someone stays for a year and I got new carpets for them and it's ruined, then I'm charging for the spots that couldn't be cleaned.

Eg.,2: If someone stayed with me for 3 years and the carpet is already 8 years old, it doesn't matter if it's completely ruined, I'm not charging for that carpet.

This holds true for everything in the house.

One of my tenants wants to get a dog and the carpet is already 10 years old. I didn't even charge more security deposits because once he lives, I'm going to replace that carpet.