That's correct, it follows the guidance suggested in IRS Audit Techniques Guide. 

First, let's define "audit-proof."

I also came to know that IRS can audit these expense and i should be ready with the relevant documents.I am looking for a trust worthy company who has done cost segregation study in past with no IRS audits . 

In other words, it very well can be challenged during your audit, but it will not be the reason why you are audited.

The potential audit risk of a DIY report just wasn't worth the upfront savings for me.

Trying to balance audit-defensibility with not lighting money on fire.

So far, the audit was defensible and nothing sketchy at all.

However, doing it yourself carries a high audit risk since you must defend your methodology without professional documentation.

In this case I would personally use DIY cost seg, they offer audit protection.

I agree on avoiding an audit trigger is critical in real estate.In my case, I went with Costseg Guys in 2025 to analyze my $300k property.