Don't take this as excoriating but it would have been wise to have it in writing. I hope you have them dead to rights but that is harder to prove without a written contract, not impossible, just more difficult. An attorney will likely be more excoriating in telling you the same thing.
If you have worked with attorneys in the past, ask one of them for guidance. Even if it isn't their area, they are generally good at directing you to someone with the proper skills and expertise. Sometimes, in a case like this, all it might take is a letter from a law firm to get the situation resolved. If the estate sale agency knows it is in the wrong, it won't want to go to court.
Yeah, that's what I'm hoping.
I actually have a lawyer meeting set up today with my buddy, to discuss wills and POA’s. I mentioned to the attorney this issue with the estate sale thief, and he is going to investigate and either take the case, or refer him to a good attorney familiar with these types of cases.