I did the same thing with the IS-6 mission; I bought the IS-6 at a discount, but waited until after the discount was over to complete the mission. (If you don’t wait, you get the discounted price in gold, not the standard price.)

How you feel about all of this depends on how you buy gold, and how much you buy. If you’re spending a fair amount, as I do, and doing it in the most cost-efficient way possible (don’t buy anything but the $99 gold package unless it gets you a) something you can’t buy in-game, or b) gives you a better rate than 250.12 gold per dollar), this isn’t a trick in any way shape or form, since you come out ahead (assuming you owned or planned to buy the premium tank anyway).

If you buy it, you’ll be getting a 7200 gold equivalent and 1080 gold afterwards (8280 total) for ~$30.
If you don’t, you’ll be getting a 7200 gold equivalent for FREE.

~$30 for 1080 gold, how about no.

I will try to get the tank, but Im not buying it to earn 1000g in the end…
playing chinks and japan is torture for me… hate those nations… As I see it I’ll end up with 5 complete nations and jap&china somewher around 10k xp …

Just change the numbers:
If the tank costs 1k gold, at 50 % discount = 500gold. You complete the mission and get 1k gold. Than you don’t get 50 % more gold (50 % of 500 = 250), but 100 % more gold than you spent.