If you never played on CSGODouble or CSGORoulettes these are simple roulettes where you can bet on three colors: red (if you win u get double coins), green (coins x14) and black (double coins too).
and there are my affiliate codes:
http://www.csgodouble.com - SOYLENT (Click 'FREE COINS')
http://csgopolygon.com(CSGODouble clone) - SOYLENT (Click 'FREE COINS')
http://csgoroulettes.com - 8WDC75 (Click 'Get Free Credits')
http://csgo2x.com- S500 (Redeem Code)
with them you will get some free coins with which you can play.
But I highly recommend you to deposit some skins to gain more coins because you don't want to lose all your coins so you will bet low bets and it will take too long to earn for knife or other worth item.
So if you have 6000+ coins you will earn coins fast with this method.
Also if you want to automate your bets use script for CSGODouble - send me a PM for it.