There's nothing misleading if the report (a) discloses the differences between the subject and a comparable property, and (b) correctly analyzes the differences so results are credible.
If the market doesn't have any reaction for the differences and buyers choose them equally, why are they not substitutes (or, if there are no other alternatives, why are they not the best substitutes)?
I own a 1,500sf townhouse, which is located in a PUD development (so this is an SFR). It is on a site of 1,000sf; that site area includes a 100sf patio and my front yard, which is only 5-feet from the sidewalk (which may exist on my lot as well). I also have a 2-car garage on my site.
My dues are $150/month, and include roof and exterior maintenance and common insurance + HOA amenities. The HOA project has common areas (no pools/etc.).
I own a 1,500sf townhouse, which is located in a Condo project. My ownership rights include the interior of the unit, exclusive rights to the 100sf rear yard patio, and there is a built-in garage which is also exclusively mine. My unit is set-back about 5-feet from the sidewalk.
My dues are $175/month, and include exterior maintenance, insurance, and my association dues for the amenities (no pools/etc.).
Other than the ownership-type, there are no significant differences between the units or the projects.
Questions:
Is it possible these two different properties might compete for the same buyer?
If so, would they be comparables suitable for analysis in an appraisal?
I'd answer yes to both.
If the subject was a condo, and other recent condo sales were available, should the appraiser only use the condos?
Sure, why not. But if the appraiser thought about it, and decided to mention in the report that the subject also competes with townhouse-style homes in PUDs, wouldn't that be a good idea (assuming it is true)?
If the subject was a condo, and no other recent condo sales were available, should the appraiser reject the SFR townhouse properties as comparables because of the difference in ownership?
No; I certainly wouldn't. If they are substitutes, I'd use them. What is my alternative: to use dissimilar condos or go back in time? Why not use what's available, presuming they are substitutes for the subject (which is what the typical buyer would do)?
(edit to add: I'd use the current SFRs and older condos; if my analysis is correct, the value indicators should be consistent and point to a credible value).