CTRs will definitely drop over time if you're super-targeting, it's a trade-off you need to make.
FB don't offer frequency capping, so if your target demographic only has 5000 members then if you're showing 10,0000 ads/day then pretty soon everyone in that demographic will have seen your ad and the CTR will drop. FB has some decent reporting though for measuring ad saturation among your demographic.
FB don't offer frequency capping, so if your target demographic only has 5000 members then if you're showing 10,0000 ads/day then pretty soon everyone in that demographic will have seen your ad and the CTR will drop. FB has some decent reporting though for measuring ad saturation among your demographic.