If you research recent sales you can always provide the appraiser a list of those sales.One of the best ways to insure a higher value is to update the property using materials and fixtures that are popular and common in the area.

What is he charging for the materials?

Most of the time, the home warranty takes a long time to approve your repair, reach the property, and then they use low-quality materials.

Licensed with permits ~$3,250.HWT standard gas single family low efficiency without exhaust retrofit $900.Sand and stain hardwood floors, natural stain $3 per sf.Paint interior walls, ceiling trim and doors 3 tone paint scheme 2 coats $3.20 per sf (floor area cost includes paint)Click lock LVT flooring install overlay inclusive of prep and quarter round $4.50 per sf (materials and labor)Asphalt roof installation 3/1 - 800 sf bungalow with 2 layers of shingles - ~$7,900Standard porch cap replacement with 2 new precast concrete steps ~$2,500Used stove or refrigerator delivery and install $350New stove or refrigerator delivery and install $HD model specificUse this as a general guideline. 

Too many flakes and dream merchants (using my material to teach while stealing your wallet and offering to help you look for it!).

My wife works for Ferguson, and I know many contractors, so I can get a lot of materials at cost.

Focus on tax-saving strategies such as cost segregation studies and bonus depreciation to accelerate deductions.By qualifying as a Real Estate Professional (spending 750+ hours annually and materially participating), you can offset your wife’s S-Corp income with real estate losses, reducing your tax liability.

There's some excellent relevant & recent material from very high quality individuals on this forum.

You can break it out by general RE activities and material participation.

While the cost can vary depending on the scope, zoning, and materials, I’ve seen similar projects run anywhere from $50,000 to $150,000, depending on factors like plumbing, electrical upgrades, and structural work.If you’d like, I can connect you with a few contractors or architects in Chicago who specialize in basement conversions.