Like Cam said.
I have in my possession a circular sash router and rebate router of identical construction to the branded Preston models, but with no indication of a maker whatsoever.
My guess is that these were either made by Preston and supplied unbranded to one or more of the big wholesalers, or else were copies after the rights ran out (or maybe even before). There are of course loads of examples (esp for planes and drills) of established designs of cast metal tools being very widely copied.
The old Buck and Hickman and Melhuish's catalogues show these tools without naming Preston as the maker, although adjacent illustrations show the distinctive patterns and logo that Preston used.
However, with the Preston brand so often making tools more collectable, and giving the price a shove upwards, it could be just too tempting for an eBay seller to make the assumption that if it looks like a Preston, it is a Preston, and should sell like one.
