FWIW, since a number of people conclude, "don't accept complex assignments - that would mean missing out on substantial income,, especially those in rural or niche/expensive custom home areas - and the reality is that with WAIVERS, complex assignments may be the bulk of lending assignments,
The main challenge of complex assignments is finding the right comps ( IMO), though there are other challenges. But, a big, expensive, or oddball home is a simpler assignment when there are comps for them, and even a small starter house becomes a complex assignment when there are few good comps.
Of course, in a rural area, larger distances are the norm, but even there, one assumes there are preferred locations or reasons a buyer would choose X location and not Y location or pay more to be in the X location- as well as some reasonable distance radius that most buyers would consider - be it 5 miles or 10 miles.(for example)
The danger with using all very far-off area comps for residential property assignments is it might not address whether the problem child subject might be an over-improvement or under-improvement. A super adequacy for tis area? If all the comps are adjusted down for location, that is a red flag for an appraisal (or if the location adjustment is evident, but was not made)
If there are no similar comps, going back 3 -4 years, within X miles, it might indicate that the area demand for these properties is low. Thus a small under-improvement house might be a tear-down for a vacant lot. The huge sf or custom or historic subject might be a super adequacy and worth less than a reproduction cost. An analysis of that has to be made, whatever one concludes.
It is a good idea, whenever possible, to use at least two closer location sales, even if they are far back in time or need large adjustments.
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