I dont think they are obliged to tell you anything that may put you off for two reasons
1) what puts you off, might not put other people off, therefore how would they determine what to disclose and what not to disclose?
2) planning applications are a matter of public knowledge, and you could have quite easily checked for yourself about any planning that was in place, instead of relying on the estate agents to do it then inform you.
I also think that if its just an application, they might well have not even put it in the first time you looked at the place, so you are also expecting the estate agents to be psychic. There is still time to comment on the application if the notices have just gone up. As to whether you can get your money back, only the estate agents can tell you