This sounds scary to someone new, but really, trial and error.

This structure is most common but could differ if your agreement is written differently. 

Also what are some common clauses to include when putting a house under contract as an investor?  

They were billing me for 2 months because they said there was an “error” due to my bank.I called my bank, there was no error.

I click on the link with that information and an error pops up so I have to call their help desk on Monday.

Those would be state/local laws and “common practice” by local judges. 

@Vlad Denisov There's common area utility charges that are going to be a cost regardless of occupancy such as hallway and exterior lights. 

Hi Adrian,I have a spreadsheet in my fileplace that has a list of nearly 500 repair items and unit prices for common repairs you would see on a rehab project.https://www.biggerpockets.com/files/user/drobertson/file/house-flipping-spreadsheet-6-liteOtherwise, JScott's Book on Estimating Rehabs also comes with a spreadsheet and is a good resource for learning how to estimate costs.

However, all recession have elements in common, and repeat.

A common practice among those too cheap or lazy or stupid to swap out a blown fuse is to put a penny in the hole and partially screw the blown fuse back in.