I am still playing because i earn most of the times, i have a net profit of 0.2 BTC, they always pay in seconds and i never had any problem. Also the house edge is only 0.1%
If you are really making any profit there than just prove it, I am quite sure that you aren't telling truth. 999dice can't be trusted because they are known for manipulating your results so they don't have probably fair rolls, despite very low house edge you will actually loss if you play with bigger bet size.