I have been able to review or been told of several audits (from other REI tax colleagues) related to cost segs in the last year or so- and of those none of DIY cost segs were allowed under audit. 

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

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 . 

Companies I've found and the cost they would charge for 1 property under 500kKBKG - $450 - (audit support included)Re Cost Seg - $1800 (audit support included)DIY Cost Seg - $495 (+ additional $195 for audit support)Would love feedback to before settling on one.

The audit support alone is worth paying for professional help.

Does anyone have personal experience with specific scrutiny of a logbook during an audit?

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

IRS audits and penalties: Studies that are poorly conducted may be full of unsubstantiated assumptions and errors that can lead to expensive audits and large financial penalties from the IRS.Long-term issues: Dealing with IRS audits and having to correct inaccurate studies can be a drawn-out, stressful and expensive process.

On one end you have a very detailed engineering studies that are highly defensible in an audit and also very expensive.  

Guessing at an 80-90% benefit without this rigor creates significant audit exposure.- Lastly, 'audit protection' from DIY services doesn't substitute for IRS-compliant engineering documentation.