Making big gains in short time is not something that can indicate ban. 1. Recently jagex relased new skill. Some people had 200m xp after couple of days, XP rates were abnormally high. No one was banned. 2. "too good to be true" is very subjective. For players with 10m gp: 5m gp/s is high For marchanter with phats and 2,1b it will not be as high. 3. Power creep is how jagex handle game. Every content is better than previous. If something was 100% legit in past then players should be safe to asume it is safe with new content. Otherwise every new content could give you ban.