It was unbearable and so bad that the entire second floor stunk like rotten eggs.

Should probably look into hiring some property management too - if you have cash flow but unbearable headaches of managing - might be better to break even and hire full-service management and then re-evaluate down the line

We have some old shag carpeting that has a faint musty smell but isn't unbearable.  

and the house is in horror condition covered with animal fesses, dirty cloths, trash everywhere, the smell is unbearable.( i was there to talk to the neighbors, but somehow their dog broke the door and got out. got on my car wont leave.

Tell them to borrow a window unit if it’s so unbearable for them or get a fan . 

Dealing with parents can be absolutely unbearable at times (great point @Mike McCarthy).And I've found that students almost always pay their rent.

If the thought of that is unbearable & a career in Real Estate is your dream you will need to look into more active aspects of the business such as becoming an agent or doing flips.

However, it's not unbearable for next tenant, but I wonder how much you would charge the tenant for the repair.

Although I will add... pictures don't capture smell, and that can make it unbearable!!        

The owner of the condo directly below me for the past 3 months has been complaining to my tenant saying the noise is unbearable and is happening 24 hours a day and they cannot sleep.