Settlers of Catan trade dynamics question
It's not a rules violation, but there are still consequences

I don't think that there are any rules against it (Catan doesn't have much to say about when trade agreements become binding), but I would consider it poor sportsmanship lie about your trading plans in order to gain information and mislead your opponents.  If you repeatedly act like this there's a reasonable chance your game group will sour on playing Catan with you.