I think siben has premium account, you have more experience and money per game.
I don't have premium, you can see it because my screens clearly say that with premium account you would have earned ...
I must say though, the level 7 aircraft get expensive. I play many nations, so i play every plane till it is destroyed. Then i switch to the next one. The repairs are getting insane after a bit.
Just play HB, pick your targets, i you have a 250kg bomb, go for the medium tank, not the AA or APC.
Play during the day, lots more noobs also for some reason.
An i am not THAT good, lol, I barely make it top3 most of the time.