They structure a list. And, run it thru to see the expirations dates. Then, sort them by dates. They then check to see if an active site is up and running. And, they also look to see who owns it.
Then, it is a simple case of buying a lot of snaps.
Also, you can do all of this with simple software likes Domain-Retrievers.
I have learned one important point on how to grap a name. Do your homework. If you wait for the list. 100 people will already be ahead of you. Then, you are forced to pay a higher price to enter the race by bidding on NW.
I get frustrated a lot. When, someone has the nerve to renew their domain name!