A couple of points--The pistol you mentioned would violate their rules as they do say you cannot list receivers or frames. Thus, I suppose the pistol frame is in violation. In my situation, they first told me that the stripped lockplate was a "complete firearm" and thus banned. When I complained to their managers, they then said it was a complete firearm because it could be combined with the stripped barrel and ramrod I was selling to make a "complete flintlock". Apparently, these are the only parts you need?!
They said something else that was perhaps more important. They told me that they rely on their customers to report listings that violate their policies and they were not set up to police it themselves. They asked me to report to them others that were listing offending "firearms" so they could be removed. I was not about to turn someone else in, and did not. However, I am certain that I was "reported" to them by someone--probably an individual who had a competing item listed. The point is, that by their own admission, they apparently only take action against listings reported to them and do not actively seek them out otherwise.