What I am more interested in, is what you would do if they didn't put the market adjustment in there? But I am not asking you answer that.
I will...
It depends.
If I thought the report made the argument persuasively enough without the adjustment and thought, therefore, the value could be relied upon, I'd make that notation in the review and refer it to my client for their ultimate decision (Just because I and the appraiser are ok with it doesn't mean the lender will still sign-off; they can always reject the deal or ask for something more).
If I thought the argument isn't persuasive enough, then I'd conclude that the report does not adequately support its value conclusion, as presented. Before I do that, I try to see if my concerns (whatever they are) can be addressed with the original appraisal in the original report. If not, the lender would then have the option to order a replacement appraisal or pass on the deal.
It really boils down to this: To sign off on the report, I need to believe, as presented, it supports its conclusions. If I do, I don't need to have everything explained in footnotes and excessive discussion. In my review, I can address my observations and lay out why, "although X and Y wasn't explained in detail" based on "A, B, and C" the conclusions are reasonable and supported.
That is one of my responsibilities as a reviewer: To provide an opinion of the quality of another's work. And I do. Sometimes, those observations are part of my due diligence requirements; typically, they are not material. But my client has to know that I actually reviewed the report; since I did, here is what I found but it doesn't materially impact the reliability of the report. A typo is a good example (and I'm not talking about "then" vs. "than"); a date might be transposed in the narrative; everywhere else, the data is appropriately identified to the date. I'm not going to ask for a correction if that one typo isn't material. But I am going to explain, in my appraisal review report, that I saw it and why I didn't think it warranted any action.
However, if an item exists that I cannot explain on my own based on what is in the report, and I cannot get to the finish line like the appraiser did, then those are the items I'm going to ask to be supplemented.
Sometimes, when I talk to the appraiser, she'll tell me, "You know, I hear what you are saying, but that's really not what I meant. I meant this...." Depending what it is, I can either say, "I get it now. I didn't get it because of this... but now that you explain it, it makes sense to me. I can deal with this in my review; thanks!" Sometimes the issue is more substantial, and I'll ask the appraiser to more fully develop that explanation in the report. Whatever is in the report, it has to convince me and the client. If it is something I can deal with in the review, easier for me to do so. If not, than I'll ask for it to be addressed in the original report.
A thought that just occurred to me is that the best way to address this with an OA would be on the phone. Written word is the worst for everyone but the most talented writers, and anyone who fits that bill is likely not an appraiser!!!
I prefer to talk direct rather than email.
However (and this may be my character flaw), I hate to cold-call an appraiser as a reviewer and start asking questions about their report. For some appraisers I deal with on a regular basis, I'll do that. For others where the interaction is infrequent, my preference is to send them an email outlining my observations, asking them to review it, and then giving them some options. Sometimes the issue is a bit complex, and it is better to discuss it; but I'll still email them first, outline the item, and ask when they are available to communicate.
In all cases, in my emails, I let them know if they have any questions, they can email me back or call me direct; or, ask me to call them.
As I said, this is a personal style: I'm just uncomfortable calling out of the blue and interrupting someone's work-flow with questions about an appraisal they may have thought was long-gone. My preference is to give them a heads-up first, so they can review what I'm asking and the report, and not be in a position to feel pressured to give me an off-the-cuff answer or response.
Walking the tightrope has been.... interesting.

And as good as I may think my people skills are, they haven't been good enough to avoid friction from time to time.