World of Tanks just introduced a new feature, the black market. In order to make that more interesting, and in line with the theme, Wargaming didn't explain how that new feature worked, you have to find out for yourself. So in case you are too lazy for that, and would like a spoiler, here it is:

The black market is accessible via the "Store" button in your garage, the one to the right of the "Garage" button. Then you have to choose the top tab on the list to the left to get to black market. And there you will find ... more often than not nothing at all. But if you happen to look either at 6 am or 6 pm, or shortly after, you will find premium tanks for sale for credits, not gold. For example I just now bought a FCM 36 Pak 40 tier III French tank destroyer for 3.5 million credits. However there are always only 20,000 of them for sale, and if you are too late, you are out of luck.

Why would this black market be interesting? Because the premium tanks for sale are tanks that aren't otherwise available. Stuff that has been in the game, but removed from sale previously, like the tank I bought. Tanks that might be a bit unbalanced: The FCM 36 Pak 40 has a crazy view range for its tier. However these tanks are by no means cheap. If you wanted to pay cash, you would have to buy gold for over 30 Euro and exchange it to credits to get the FCM 36 Pak 40. The previous tank M 41 90 mm GF was 5 million, or about 50 Euro.

However most people who will buy these tanks probably won't use their wallet. Because you are only short of credits if you are playing for free, and/or advancing through tech trees, constantly buying new tanks. If you have a premium account and mostly play your favorite tanks, without using much premium ammo, you might easily have millions of credits accumulated. The recent patch 1.5 added another 10% to your credit earnings for premium account holders. In consequence some people shoot premium ammo even when it isn't necessary, just because they can easily afford it.

In short, the black market is probably designed as a credit sink by Wargaming, to remove excess credits from the World of Tanks economy. That is probably a good idea, but it has its pitfalls. I just played a tier III game, which had several FCM 36 Pak 40 on each side. As these tanks are very slow, and powerful mostly when hiding in a bush and using their superior view range, both sides ended up camping in the back, which makes for very long games, and more draws. I do hope that once the first excitement over these tanks is gone, they get a little less frequent.