Clearly the problem is not account sharing: it asks a too much good organization. In theory, it seems feasible but this game is quite personal (ie collect cards) and I don’t see how one player want to share with someone who you don’t really know.
If we are talking about that, it’s maybe because some players were saying that they were sharing account but in fact, they were using bots.
So yeah the real issue is botting and any suspicious activity should be shared with the community 
.
But it should be a detailed call out like this topic:
Devs don’t have so much time to update their automatic botting detection. And you should know that cheating is a race between devs and cheaters: as soon as devs improve their detection, cheaters improve their bot. And it’s looping like that.
So @Sirrian, @Saltypatra how can the community help you? Do you have a detailed guideline for reporting bots?
Last point about PVP, it asks a crzy amount of time to be in the top and I believe it’s totally out of what devs thought it would be. It’s maybe why devs don’t care that much about the PVP leaderboard and why they are focusing on a new leaderboard, the GW one.