The situation you are describing definitely happens, people have their mates they like working with and a single relationship can make a whole career. Normally

The situation you are describing definitely happens, people have their mates they like working with and a single relationship can make a whole career. Normally though, such relationships do not involve the sales person charging significantly above market rates. The client usually has very strong incentives to reduce costs. While a single salesperson might build a career on a chummy relationship this isn't a sustainable approach for an entire firm to take because it is too unusual. The majority of the revenue is coming from client/sales relationships where the client is at least somewhat price sensitive and sufficiently savvy to get more than one quote.