I don't get it; why would it be _more_ of a problem than with current tax & benefits systems? Politicians can already make the "increase $benefit"/"decrease $tax" their #1 policy.
But they can play a constant shell game with those, distracting you with this one while backtracking on this other one. UBI, IMO, would unify these various systems and eliminate the distractions that allow them to make these promises while not really keeping them.
If you think this will force politicians to keep their promises, as opposed to breaking them in broad daylight, you need to pay more attention to politics.
UBI making shell games like that harder is a good thing if you ask me.