There are safeguards in place and it's early days, so there are always going to be issues. Still, there's a dark sense of inevitability when the first mod in Valve's new paid-for category is removed.
Skyrim's fishing mod, from Chesko and aqqh, was removed shortly after it was revealed the creators hadn't gained permission to sell from another modder whose assets were used in the fishing add-on.
As you can now see, the page for the mod shows nothing aside from a couple of discussions; comments were deleted before the mod was removed. Fortunately the print-screen button exists:
These images – thanks to Destructoid – show where the issue came in. People were profiting from something another person had made a part of, and that person didn't want their work to be sold for profit.
Simple, and totally fair on Fore's part as far as I'm concerned. This is unlikely to be the last time an issue like this pipes – the early days of Steam's foray into paid-for mods could well be a bit of a minefield.