Scope of work issue. Also, take a look at S.R. 1-4; "In developing a real property appraisal, an appraiser must collect, verify, and analyze all information necessary for credible assignment results." If you can do a credible job using whatever data sources, then you are probably ok. If you don't verify properly, and thereby use bad info to arrive at a result that isn't credible, you have a problem.
And, just because other appraisers are doing it, doesn't mean it's ok. Definition of 'appraiser's peers' is; 'other appraisers who have expertise and competency in a similar type of assignment". If others are doing a job incompetently, doesn't mean you can too.