Legal Question in Wills and Trusts in Pennsylvania

Why would the heir do this at all? There should have been an agreement.

You ask if its "legal." It is not defined as a crime. The question is not whether its "legal" but whether it is proper. I don't know what kind of documents you are talking about. If an inventory was filed listing the appraisal price but the home sold for more at a later date, I don't see a problem. It is not at all obvious (based on the limited information that you have provided) that the executor is acting underhandedly and "keeping" the profits.

An accounting must be filed in order to close out the state. The accounting would have to list all money received by the estate and any distributions. Depending on the county, the accounting would have to be confirmed by the court clerk or a judge. The beneficiaries have to acknowledge that the accounting is either ok or they have to file written objections thereto. Obviously if the proceeds of the land are not fully disclosed in the accounting then the beneficiary needs to object to that.

You ask what the heir can do. The heir needs to consult with his/her own probate attorney who practices in the county/state where the estate is pending. I would pay the attorney to review the estate file and what has been done to date to see if there has been alleged misconduct as you claim. If a final accounting has not yet been filed, the beneficiary should get notice of it. I would also pay the attorney to review it when it arrives. If things are not in order, the attorney should object to the accounting.