I agree with you. FSDO 19 apparently disagrees. From the Facebook posts by the attorney for the pilot against whom action is being taken:
The aviation safety inspector who started this whole thing has said that, in FSDO 19, they will enforce this policy against aircraft like the PA32 that can be used for charter of cargo, whenever they find them with the seats removed as they come in through Customs. I am not sure that this was an authorized statement of official FSDO policy.
The FAA attorney seems to have adopted the position that, unless there is an FAA approved “seating configuration” for every possible combination of seats being removed, it would require an STC (a 337 field approval will not do) to fly the aircraft without any of the seats in place (except the 7th seat which is an option in some models). We do not believe this to be an accurate statement of the law. We believe that all that is required, in an aircraft where the seats are designed to be removed easily, without tools, and where the manufacturer has provided the weight and moment arm for each seat and directed the pilots to make weight and balance calculations for seats removed, is that such weight and balance calculations actually be made by the pilot prior to flight. Of course, Part 91 does not require that the physical calculations be recorded and kept. But, in an abundance of caution, it would seem to be a very good idea to keep a written copy of the actual calculations you make for flight with whatever seats you have removed.
The owner of the aircraft has a house and a business in the Bahamas (the house was badly damaged in the last Hurricane). He takes supplies and materials with him in his aircraft. No compensation or hire at all. But the complainant thought that the aircraft, being loaded (in his words “to the gills”) “must” be being used for charter. The ASI put the N number on a watch list with Customs to try to catch the aircraft doing illegal charter. But there was no evidence of charter at all. So the ASI decided that the absence of the rear seats was an Airworthiness violation, even though there were two W&B forms in the aircraft — one for all seats installed; and the other with just the two front seats installed.