The photos will show both bathrooms were not changed except for floors and plumbing leaks. 

One thing to make sure of while you are doing the fixes is that things are permitted that need to be (plumbing, electric, structural items, roof) because down the road when you sell your property disclosure may ask if items repairs were permitted.  

For considering deals, your buyers are going to want to know stuff like repairs that need to be made, condition of major things such as roof/HVAC/plumbing, property ARV (After Repair Value), a few comparable properties for the ARV you came up with, and plenty of quality pictures of the property.

You can get a warranty through HomeServe for plumbing and sewer lines for less that $20/mth.

This will help you get a better idea of what tile, hardwood, carpet, plumbing fixtures and light fixtures costs for your rehabs.#3 Contact Local Contractors for Labor PricingCall local Subcontractors and get budget pricing for common repairs on your typical rehab project.For example, call a roofer and ask what their average cost per Square of Architectural Asphalt Shingle Roofing would be on a 1,500 sf house, with a 6/12 pitch.Note: Some contractors will be reluctant to share pricing without seeing the property, but tell them you are just looking for a rough budget number you can use on future projects.#4 Compile Your Prices into a Spreadsheet or Estimating SoftwareOnce you start to get a better understanding of Labor and Material costs you will want to store this data into a spreadsheet or software that you can use to help you streamline the estimating process.The Book on Estimating Rehab Costs comes with a spreadsheet that you can use to help you populate your own database of labor pricing and material pricing.

What have been the most effective methods for you?

Thank you @Cody Neumann I will use this method too.

They forget long-term maintenance like hot water heaters, plumbing and roofs. 

General plumbing and electrical stuff.

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