However, I found out I had to clean up that messy house (lots of trash, like a hoarder's house).

Water is a bad thing if not addressed or cleaned up as quick as possible. 

If the upstair tenant is in volition of the lease you could hold them somewhat more accountable to their children during those hours.I agree kids are kids and thick carpets or rugs may be your best response.

There was recently a water intrusion event caused by a clogged drain outside which caused some hydrostatic pressure in the soil and some water came up through the slab, which the tenants promptly cleaned up and I ran a dehumidifier I rented from home depot for 24 hours.

Is Homeaglow an option for Short term cleaning services?

I try to have my rentals be weed free (properly remove any weeds), as I have seen some CRAZY weed yards, and simple/clean as possible. 

If it's just surface mold that can sprayed, washed, and cleaned up that's way to high. 

Went through Kaydem Credit to clean some things up on my credit so I would be stronger the second time around.

However, on move-in day, the tenant claimed the unit wasn't clean enough and refused to move in, despite my offer to clean whatever was needed the next morning.

Property appraised for 245k; however, it was classified as a c5 which prevented most lenders from issuing conventional financing.I contested the appraisal and the appraiser held their ground, but their supervisor told me that if I slapped a coat of paint on the cabinets (these needed to be replaced due to wood rot) it would be an easy c4.I paid $520 for a new appraisal, contacted all my family and friends, deep cleaned the home and put a fresh coat of paint on the rotted cabinets and over the doors.