Short answer

A cost segregation study can fail an owner in two places: in the sales pitch, before any work is done, and in the report, after it is. The IRS's Audit Techniques Guide lists the elements of a quality study and tells examiners what to request, so the red flags are not a matter of taste. Each of the twelve below is the absence or the inversion of something the guide expects, or a claim that the professional rules do not allow. Some are disqualifying; some are questions to ask. None of them is proof of bad faith by itself, but each is a reason to stop and check before relying on the study or paying for it. This article is general education, not tax advice, and it names no providers.

In the pitch

1. A result before the documents. A percentage or a dollar saving quoted before anyone has seen the closing statement, the drawings or the building is a rule of thumb, which the guide treats as the least reliable approach. A practitioner can quote a range with a caveat; a promise is a flag.

2. A fee tied to "savings." The saving depends on your return and on the passive activity rules, which the practitioner does not control. Practitioners who practice before the IRS are also subject to Circular 230's restrictions on contingent fees for most return-preparation work. Ask your adviser how the fee structure interacts with the rules that apply to them.

3. Government approval. "IRS-compliant," "approved," "certified by the IRS." No preparer, method or product is approved by the IRS for this work; the guide describes expectations, not endorsements. Advertising must be truthful and substantiated, and the professional rules prohibit misleading solicitation. This one is disqualifying.

4. No site visit for a property that warrants one, with no explanation. The guide lists documentation and inspection among the elements of a quality study. A practitioner may reasonably skip a visit for a new building with complete records; the report should say why.

5. A projection with no passive activity line. Rental losses are generally passive. A projection that shows a first-year saving without stating whether you can use the loss is not modeling you.

6. Pressure to bypass your adviser. The study is an input; the adviser decides the return position. A practitioner who wants to file for you, or who says the adviser is unnecessary, has stepped outside the study.

In the report

7. No identified preparer. The guide's first element is preparation by an individual with expertise and experience, with credentials referenced. A report signed by a company name only, or with a limitations paragraph disclaiming individual responsibility, is missing that element.

8. No methodology section, or a methodology that is a percentage. Ask which of the guide's approaches was used. If the report cannot say, or if component costs are all fractions of the price rather than quantities times unit costs, it is a rule of thumb dressed as a study.

9. Land allocated without evidence. Basis is allocated between land and building by fair market value at purchase; the guide addresses the allocation specifically. A land line with no appraisal, assessor ratio or stated method is the most common error in small-property studies and undermines everything below it.

10. No legal analysis for classifications. A list of assets and classes is not a study; the reason each item is section 1245 property or a land improvement is. If the report has classes but no reasons, the examiner will supply reasons of their own.

11. No reconciliation, or a residual that hides the difference. The guide lists reconciliation of allocated costs to actual costs among the elements. A study that does not tie to basis, or whose building residual absorbs whatever the components missed, cannot be checked by anyone.

12. Dates that do not match the documents. The placed-in-service date set to the closing date on a property renovated before renting; 100 percent bonus depreciation applied to property acquired under a contract signed before January 20, 2025; a renovation folded into the original building line. The dates are examined every time.

What to do when you find one

FlagResponse
1, 2, 3, 6 in a pitchDecline the engagement; the professional rules and the guide are against it
4, 5 in a pitchAsk for the explanation; proceed only if it is written into the engagement letter
7, 8 in a reportAsk for the preparer's identification and the methodology; if unavailable, treat the report as a rule of thumb
9, 10, 11, 12 in a reportAsk for the evidence and the corrections; a competent practitioner can supply them, and a product cannot

A study you already relied on that shows flags 7 through 12 should be reviewed by a practitioner against the guide's elements. Where the property still matters, a proper study can be applied through a change in accounting method with your adviser; where it does not, the review at least tells you what you would have to produce.

Using the list

Take the twelve flags to the pitch meeting and to the draft report. Ask about the pitch flags before signing and about the report flags before accepting the deliverable. Write the answers down; an engagement letter that records what the practitioner promised on each point is worth more than any assurance given in conversation, and it is what your adviser will rely on if the study is ever questioned.

What is not a red flag

  • A limitations section that discloses estimates, judgement and scope. That is good practice.
  • An estimate-based study on a purchased building with no records, disclosed as such. The guide accepts engineering cost estimates when records are unavailable.
  • A fee that is higher than an online product's. Scope costs money; compare the sample report, not the invoice.
  • A practitioner who says a study is not worth it for your property. That is the advice you want.

What people ask on Reddit and other forums

Owners post pitches and reports in the "cost segregation reddit" threads on r/realestateinvesting and ask whether they are being taken. The searches that lead people to these threads are usually phrased "cost segregation red flags", "cost segregation scam" and "bad cost segregation study".

"They promised 30 percent before seeing anything. Scam?" A promise before the documents is a rule of thumb, whether or not it is a scam. Ask how the figure was derived; if the answer is experience with similar buildings, it is a range, not a result.

"The fee is 20 percent of my savings. Normal?" Ask your adviser about the professional rules on contingent fees and about who computes the saving. The saving depends on your return, not the practitioner's model.

"The report is four pages. Is that a study?" Ask for the methodology, the asset list with reasons, the reconciliation and the workpapers. If they do not exist, it is not a study in the sense the IRS guide describes.

"They say the IRS pre-approves their method." No provider, method or product is approved by the IRS. That claim disqualifies the provider.

Questions people also ask

What is the biggest red flag in a cost segregation study?

A promised result before the documents are seen. Everything else follows from a method that starts with the answer.

Is a percentage-of-savings fee a red flag?

It deserves care: the saving is not the practitioner's to know, and the professional rules restrict contingent fees for most return-preparation work by practitioners before the IRS. Ask your adviser.

Can a study be legitimate without a site visit?

Sometimes, for a new building with complete records. The report should explain the decision and its effect on reliability.

What should I do with a bad study I already used?

Have a practitioner review it against the IRS guide's elements, tell your adviser, and consider a proper study applied through a change in accounting method if the property still matters.

Are all cheap studies bad?

No. Price is not the test; the presence of the guide's elements is.

Sources