Buyer's agent misrepresented buyer in financial qualifications?

You can't sue and win. This one is as much your fault as it is anyone else's fault. Did you ask for any written evidence of this buyer's qualifications before you jumped at the offer ? I'm not sure if you are represented by a qualified agent. If you are, your agent should have advised you on this. If you went it alone, without an agent, you are now learning the pitfalls of real estate transactions.