The whole appraisal infrastructure is a complex system of many feedback loops.
If TAF created a standard that covered in detail the protocols of the different appraisal methods, without ambiguity, without allowing contradictory interpretations to be drawn, appraisers would be able to more safely do appraisals and avoid the risks they currently have dealing with lenders. The lenders themselves would indeed have to alter their behavior whenever it conflicts with USPAP.
GH - you are always putting the cart before the horse - on this forum very often kowtowing to the lenders with respect to appraisal issues under the pretext that they are making the so-called "decisions" for which they need an appraisal. The job of the appraiser is to take the SOW from a client, run it against the standards and regulations to eliminate unacceptable portions of the SOW, send the corrected SOW back to the lender/client, - and if he agrees to the changes, then objectively perform the required appraisal.
So, by altering the USPAP standard, of course TAF can effectively alter lender behavior.
Unfortunately the USPAP standard is so lax, it gives the lenders great latitude in requesting changes to reports from appraisers, as well as great latitude to attorneys hired to sue appraisers.