Since it's an UW req, we're stuck with it on lender appraisals. And yes, generally, comps in subject building/project are given the most weight...though in small buildings or a unit that's unique one has to go outside anyway.
But, the MV definition stressses an open and competitive market. While one building can make a market unto itself, it is not the standard of an open and competitive market. Client wants to see what competing units are selling for, even if they need adjustments up or down, it at least shows them a reference outside of subject building itself.
Sometimes appraisers don't look hard enough for a viable outside competing comp, they just stick one in to fufill the req and give it no weight. Often, a competive outside comp is out there, you may have to exapnd the search a bit.
Consider charging more...condo assignments can take more time, just trying to verify the building information is a job in itself. That annoys mre much more than trying to find an outside comp. The lender sends out a condo questionaire anyway, so they are getting the information twice, why do they need the duplicate information from us?