I'm a lawyer. This is not legal advice, you must pay for that. There is no client-attorney relationship created.
There are certainly steps that you can take if you want. Do you have the buyers info? Name/address/phone etc? There are things you can do without a lawyer that may work, but probably not - one of those things where the only thing you are spending is your own time. i.e. sending them a demand letter.
That you had a contract signed, a deposit and full balance paid and they backed out really would annoy me - and if it were me - I would pursue them out of principle with the realization that I know its not worth my time to do so but still would do it anyways. Now it doesn't cost me anything to hire myself, but you can do things yourself with minimal knowledge and cost if you want. Most important thing though is if you have the buyers info. PM me if you feel like pursing it further and want to talk.