You just received two good pieces of advice:
Dave points out a likely cause (one which I commonly see when I review) why there could be the "5%" difference!
Jay puts in common-sense language that the review process is about quality and credibility of someone else's work, and not personal style. Chances are better than not that if all four of us appraised the same property at the same time using the same data, we would come up with different values; assuming we know what we are doing

laugh: ) all of our values could be reasonable, and you and I might differ by $40k!
To put it another way, let's say that "accurate" market value of the subject is between your estimate and the original report's: $820k. Now, the difference between your estimate and the original report's vary by 2% from the "accurate" value; If I was within 2% of the "accurate" value with consistency, I'd have every court, lawyer and mediator in the country calling me for value determinations.
If the report's quality is good, and unless the value concluded is not credible, I'd accept it.
In such cases, I'll make a statement that in my opinion, the original report's value is at the upper end (or, very high end, if I think this is so) of the reasonably supported value range. That's my review style; may not fit for others, but it tells my clients what I want them (and what I think they want) to know.