If you're running a study like this and want to ensure a certain result to support your take on the issue it'd be easy to pick recipients to reinforce whatever your goals are. IE. only choose people with stable employment who won't all quit their jobs immediately when they start getting checks, or the opposite if your goal is to sink UBI.

This is the political equivalent of paid Amazon reviews. The goal is to be the winning despot for a socialist regime. It's like the lottery, but for power. They're never going to stop these "trials" until anti-bribery laws are updated to include false philanthropy.