There is a special going on on the EU server to allows players to trade in their premium tanks for 50% of their gold value and that automatically deducts that gold amount from any premium tank that is available in the tech tree. Quite nice for tanks that you regret buying, but of course you still lose gold effectively. Available from today until the 16th of May.
Source & more info: https://worldoftanks.eu/en/news/special-offers/trade-in-april-2017/
I have for instance traded in my HT No. VI as it didn’t live up to my liking. I have traded in it for an STA-2; whereby I had a reduction of 1,875 gold (total price: 5,525); plus the compensation of camos I got in 9.18 (2,400 gold); I “only” paid 2925 of my own gold to get a tier 8 premium tank.
Please note you can also trade in your mission tanks (T28 HTC is worth 3300 gold in the trade in for instance).
Vehicles that can be traded-in