starts farming my camps - nothing punishable with someone farming jungle camps on either side. Jg does not own any camps nor does laners own any minions. Someone taking jg camp or lane creep is not punishable even if doing it intentionally or otherwise.
flashes in spawn - while you may know he's trolling, how does the system differentiate this from someone accidentally uses flash or any other summ? I've accidentally flashes in the fountain many times when trying to type to team without pressing the enter key first (uses ult and other spells too). It's not indicative of a troll or at least not easily detectable.
sells items and starts running into the enemy - THIS would get someone detected by the int detection system IF someone doing it blatantly
Did you report? On what basis do you guaranteed that he will receive no punishment? Or do you just "feel" it?