“...an important duty to carry out justice...”
Marcher Lords were accountable to no-one in how they ran their lands – this was one of the special powers granted to them. However, they were not tyrants. The medieval world used law courts and witnesses much like today.
“...the Court is a nice money maker...”
The Pembroke county court was an important source of revenue for the Earls. There was a fee for presenting any case, plea or petition before the court, and the fines imposed also went into the Earl’s exchequer. Neighbouring lords were very protective of their legal jurisdictions, and often clashed with their neighbouring lords over whose court a case should be heard in.
“...Most people get off with just a fine...”
Today we consider medieval justice to be harsh, but not every crime took people directly to the gallows. A Lord had good reasons to impose fines rather than executions, as it combined both punishment for the convicted and profit to himself.