Here's something I discovered recently. If you're playing WoW (World of Warcraft) on Linux using Wine, the in-game shop will give a black window and won't work.

As it turns out, it can be a problem even on Windows. Thankfully, a random post from a Linux user in a Windows support topic gave the answer.

In short: ensure your WoW install folder is setup as a drive letter in wine config. Instantly fixed it on my end.