@Rachel Degennaro
At this point, you should probably talk to a lawyer that can really spend the time to review your facts to see what options are available. One of the biggest decisions you have to make is whether you want to sue for specific performance. Based on the facts you wrote, it sounds like you may have a good basis to demand specific performance. Whether it is worth your money and time is a different matter.
You can also sue for monetary damages. But it’s one thing to get a judgment --- it’s another to collect on it. So you would need to do some research on that end as well.
If you decide to pursue legal action, you would obviously bring the kitchen sink to the buyer. This includes the RESDL claim that @Steve Babiak mentioned. Whether it's going to stick is another matter but there is nothing inherently inconsistent about seeking both specific performance and a RESDL claim.
In terms of magistrate versus Court of Common Pleas, nothing that happens at the magistrate court level really matters if the defendant will appeal the judgment to the Court of Common Pleas. Given that this seller has a lawyer, just note that getting a judgment at the magistrate level may mean little.
This has happened to me many times; both as an investor and as a lawyer. It's obviously infuriating at an emotional level. But you also can't have your emotions cloud your judgment.
Disclaimer: While I’m an attorney licensed to practice in PA, I’m not your attorney. What I wrote above does not create an attorney/client relationship between us. I wrote the above for informational purposes. Do not rely on it for legal advice. Always consult with your attorney before you rely on the above information.