I didnt know if this method just for rooted device/not.
1.Use modded apk and gather as many gems from lucky box/rune box that cost 50 gems. Other than 50 gems transactions, ur acc will be banned. For faster gathering gems, expand ur inventory for 200gems max. Do this as many you want.
2. Install clean apk over modded. Bought any chest you want from increased gem. Vice and versa.
Still didnt got ban hammer with this method.