Guild Gun is a very generic term. It should simply imply a gun that has no markings other than the proof marks. Many so called "Guild Guns" actually have a maker's mark. Don, Rocketman, has developed a spreadsheet to calc the value of a gun. One of the elements in the formula is Brand Value. A guild gun has no brand so the value drops. A gun proofed in London does not carry any special value unless you see the name H&H, Boss, etc
Having stated the above... I have seen major dealers brand a gun as guild simply because they did know the maker or more likely did know how to id maker's marks, etc.
There is one locale that is an exception to the Guild Gun / Brand Value relationship, that is Ferlach. They felt no need to put their mark on a gun in most cases. The mere fact that it had Ferlach proof marks was enough.
Pete
