It is best to ask if the Landman is a Certified Petroleum Landman. That is the highest level of expertise and requires extensive training and an agreement to abide by ethics standards. If they are not, then ask for someone from their firm that is.
Many landman no longer work directly for an oil company. Those days are mostly over. Most landmen work for land companies that are hired by an oil company or are independent contractors so the link to the actual oil company is no longer there.