This has been and probably will always be a relationship based industry. If you take a look at the most successful contractors in this industry they always have a roster of key clients which keep them working. You can also see it in consolidations when one company buys out another company. The acquirer might get the equipment and personnel but without the key relationships they don't really have squat. You can't have your new corporate salesman all of a sudden call on a 30 year client and say "Hiya buddy let's go play golf!"
Networking is by far and away the best marketing out there and in terms of expenditures vs. revenues it is really cheap.