It's always fun finding pirates and fakery on auction sites. The latest such instance is this Sonic and Knuckles 5 cartridge for the Famicom, found on Yahoo Auctions.
The cartridge has a random smattering of official Sonic art, with the text "Super Sonic 5" at the top. The title screen contradicts this, displaying the words "Sonic and Knuckles 5". I have to say that the title screen is rather impressive for a NES, being ported quite well from Sonic and Knuckles.
The game itself is a rather common pirate, seen under various different titles - most frequently Sonic 3D Blast 5 and Somari (the latter with Mario sprites). The screenshot in the auction is of Spring Yard Zone, although those blocks don't actually move.
Overall the game is quite an accurate port of the original Sonic the Hedgehog, more so than the Master System version. However, it certainly doesn't play, look or sound as good as the Master System version.
The seller has predictably listed the game as "rare", which can be bought now for ¥14,800. That's £101 for all those interested in the UK! I think you're better off hunting down the ROM.
[Source: Sonic Retro Forums]