This is not legal advice. For legal advice see an attorney.
In most cases purchase contracts are written to favor the buyers. The buyers normally have a set time period to secure financing (called the contingency period), inspect the property, etc.
If the buyers did not remove the loan contingency, it is doubtful that you could prove damages....that you turned down another offer because you were dealing with them.
If a Realtor was handling your transaction, my assumption is that the MLS status of the listing was BackUp Offers, or Contingent taking back ups, so the property was still being actively marketed until the buyers remove all contingencies.
I would focus more on talking with your Realtor.
1. Review the offer paperwork and see where they were in the process when they canceled
2. Discuss you problem with your Realtor. You can even show them this post. As a listing agent it is possible, in the final counter before acceptance, to REQUIRE that the buyers Co apply with a lender known to either you or your Realtor. It is does not obligate them to use the lender, but it gives you some control over the process.
3. Depending upon your market conditions, you can also impose a per diem fee for every day late that they transaction closes (once contingencies have been removed).
I would also review all properties with whom you are competing since putting your home on the market and see how many have either lowered prices or sold.