You don't play a plausible deck because you need several accounts to make it work (6 if you want to do it quickly), and you don't want to spend 100s of tickets on decks when you could spend 2.
It should be trivial for WotC to catch people doing this by looking at their match history, regardless of what decks they're running. Someone running this scam is going to be paired with a cyclical group of players over and over again, which would be impossible for a regular player.
If it makes people feel any better, this doesn't affect league results or prizes for any legitimate player. It's effectively like someone telling WotC they ran an FNM to keep the WotC-provided foils.
Vintage players should just keep it in mind when they make decisions based on published decklists
@john-cox that's the gist of it, but consider that you can be logged into MTGO with two different accounts on the same computer, and that the match doesn't start until both players see that a pair happened and click "join". It's trivially easy to do this by yourself with almost zero chance of being paired against a real human by accident.
For those curious, this thread is very informative: https://twitter.com/TheMaverickGal/status/1131335618418663427
Kendra Smith is also signal boosting the current issue in Vintage with Magic Online and many of the big venders tagged, so hopefully that helps with swift action.
Are they already getting more sophisticated at this and playing decks that look slightly more real? The MTGO player Buneca, who ran that Heartless Summoning deck, just placed twice in the 7/21 League with this Bolas's Citadel list and with this Mystic Forge list. It's possible these are legitimate finishes, though things like 16 Swamps and sideboards composed entirely of "search your opponent's library for cards and exile them" effects make me pretty skeptical.