I believe by and large they don't pay the price because nobody really cares. The British certainly don't like it, but it'd be a very different story if the Russ

I believe by and large they don't pay the price because nobody really cares. The British certainly don't like it, but it'd be a very different story if the Russian agents were murdering Royals or British politicians. If they're "only" murdering exiled Russians, it's more like the Turkish intelligence services murdering Kurdish activists in France: not amused, but definitely not something to go to war over. You're right, there are lots of people who "believe" them, but I think that's a somewhat different story. There's a group of people we've left behind in the West that will believe whatever you tell them, as long as it vaguely resonates with their world view. They dislike their country's government because of their personal situation, so if you start your tale by "your government is lying to you", you have their attention. I don't know how to win them back, but I don't think they actually 'believe' it, it's more of a tribal thing, and they've switched tribes because they didn't feel like they were treated as part of their original tribe (which I can understand to some degree). It's important to say though: these people 'believe' those tales precisely because they're powerless; what they believe or don't believe does not matter. It's not like the Russian military would blow up a nuclear power plant to irradiate the area and have radioactive clouds drift westwards and we'd hold a plebiscite on how to respond (thank god!).