So, in reality every month your moving close and closer to sucking out months/years of profits via items aging out, cap-x coming to bear. 

What were the biggest line items?

The other business I run is reselling, listing items on eBay & FB.

.* No calls accepted to review receipts: I have asked Jenny several times for the last 3+ weeks to get on a call to review the receipts and all of the items that are in the house, I have given her several deadlines to resolve the issue, she has never accepted any of my invitations to join any calls despite me pleading her to do so as my credit card payment is now due and has a 29.99% interest rate if not paid.I have found several people that were also affected with just 2 facebook posts.

Also, what others have said, the personal touches on what is in your place (e.g. providing all the essentials instead of having people buy TP, coffee, shampoo, etc.) and the quality of those items (no tattered towels, stained sheets, etc.).  

@Steven Catudali don't understand the value that he is bringing... those are all just items you can pay a professional for. 

I've been pondering the same question lately.For items like HVAC filters, do you remind tenants when it's the time to change it, or just expect that they will do it?

Tenants should pay for that.My lease considered normal to be a few items hung using 1" nails or smaller.

There are a lot of options out there.Some of the most useful items BiggerPockets members have identified are features that save time so they can spend time working on their next property.

I'll Google those items and see what I find.