To expand on Steven Santora's response above...
In the event that a reviewer is asked to express their own opinion of the value as stated in the original report, the reviewer is allowed to rely on and base their opinion on the original report to the extent that they agree with that report. If there are any areas of disagreement, the reviewer is not required to start from scratch and produce a new appraisal report; they can simply rely on those areas of the original report with which they agree and then separately develop/correct those areas deemed to be insufficient.
Let's take your case as an example. Let's say that as a reviewer, you agree with the sections of the original report that describe the subject property, including all of the front page, the diagrams, plat maps, location maps, etc. For whatever reason, you disagree with the factual description and use of Comparable No. 3 in the Sales Comparison, but not necessarily the final conclusion of value. In expressing your disagreement with this item, you are required as a reviewer to explain why you disagree with that comp (in this case you say it isn't a sale). If that affects your opinion of value or if it so significantly detracts from the reliability of the rest of the appraisal report, you may not have enough information at hand to develop an opinion on the value conclusion. Just because the client wants one anyway in no way mitigates your problem of lack of reliability.
If you decide to disagree with the analysis and the final value conclusion, and present your own version of things (in other words, to "fix" the appraisal), you need to develop that different opinion by presenting and analyzing the extra data using the same reporting standards as the report being reviewed. In this case, an extra comps page with one or two more sales gridded out and the appropriate reconciliation, along with an accurate scope of work for your review report would be sufficient to cover the bases. No need to do a new appraisal report from scratch.
If there is enough doubt of the overall reliability of the original appraisal and appraisal report because you have evidence of dishonesty, you have the option of recommending to your client to completely reject the appraisal (because its incurable) on those grounds and expressing no opinion of value in your review. It's when you do express your opinion of value or agree/disagree with the value conclusion that you are held to the same reporting formats as used in the original work.