"Mushroom brands" (also referred to as "myth brands"), so called because they pop-up overnight and often disappear just as quickly, are watch companies which are completely outsourced to a high-volume Chinese manufacturer e.g. MillionSmart Enterprises and then sold exclusively over the internet. Myth brands often feature European sounding names and claims of European origin, elaborate tales about the brand's namesake, and sky-high listed MSRP's - but are then always "On Sale!" for about $100.
For example, let's assume that "Chevalier" is a watch brand found only on eBay. "Chevalier" watches on eBay are listed in the $100-$300 range, despite featuring skeletonized or complicated movements similar to those typically associated with high-end Swiss watches. Some of the dials and cases may look very similar to other mechanical watches listed on eBay in the same price range. The listing says that "Chevalier" is 'Located in Germany' and the word 'Swiss' included in the listing title. One particular model looks like it may have a Swiss ETA movement - and is listed at a much higher price than the others.
In this example, we could quickly conclude that "Chevalier" watches are Chinese watches, whether or not the owners of the brand are based in Europe. We can also conclude that use of the word Swiss in the eBay listings is both misleading and almost certainly false. Coupled with the fact that "Chevalier" does not exist outside of eBay, we can now make an informed decision as to whether or not we would buy a "Chevalier" watch at all, and if we would, whether or not we would buy one from a dealer who either does not know their product or (more likely) who deliberately misrepresents it. Caveat emptor.