You search battle list for clan less kingdoms. Then look at their wall. See whether any activity in last 10-20 days, if no activity, it's safe to say he/she is inactive. Go ahead n hit 5x, test again in 24-hours, if there is retaliation, apologise and say you're hitting him off BL. If no retaliation in 72-hours to 5-days, it's a given that the kingdom is inactive, please go ahead and unload full bars every hour. ^^^ I've just given you the way to find and keep inactive kingdoms. Sometimes I'm really lucky and come across entire full inactive clans. Great fodder for growing clans. Enjoy!
Battle List only shows players online currently or within the last 10(?) minutes, not inactives, sorry
Another easy way is to search thru ally list and start writing down names of pure spies. I search around 400-750b range. Usually find a small list of pure spies. Some even with allies. Like my current osf. Has trillions in allies as a pure spy. nOobs these days lol