Here's an article with additional FAQs on cost segregation studies that you may find helpful.

MLS, knowing my numbers, knowing the market, studying the listing, and having a team in place.

I recommend you print, study, and highlight the HUD guide: https://www.hud.gov/sites/dfiles/PA/documents/HUDAsstAnimalN...You should also check with a local HUD office to see if they have any additional guidance they can provide you.Keep in mind, not everyone is subject to Fair Housing requirements and you may be exempt from allowing the ESA! 

It proves if the tenant is current on their rent and theirhistory of whether they’ve paid on time or not.

Find Investment OpportunitiesMarket Research: Analyze local real estate market trends, property prices, rental yields, and potential for appreciation.Network: Build relationships with real estate agents, investors, wholesalers, and property managers who can provide leads and insights.Due Diligence: Conduct thorough inspections, financial analysis, and feasibility studies before making a purchase.6.

. § 1.469-5T(f)(4) provides that reasonable means for proving hours may include a statement of services performed AND approximate hours based on appointment books, calendars, etc.

Study the market.

Can they prove how long it takes to rent a vacant property?

Definitely don't trust them to do what they say since they have a history proving that would be unwise.

If you sue I think you would have to prove damages I believe.