Broker, buyer, and the words in between.
The phrase "mineral rights broker" gets used loosely, and the distinction it papers over is worth understanding before you choose anyone. Broadly, there are two models.
A broker markets your minerals to a pool of potential buyers and is typically paid a commission out of the proceeds. The appeal is reaching more buyers; the tradeoffs are the commission and, often, a longer process. A direct buyer purchases for their own account. There is no commission layer and the process can move faster, but you are working with one party's view of value rather than a marketed auction.
Neither model is automatically better, and good and bad actors exist in both. One of the most useful things you can know about anyone you talk to is simply which model they operate under and how they are paid, so it is worth asking directly and early. A counterpart who answers plainly is giving you the information you need to compare your options.