Volume buying typically involves using a computer program to automatically search for available domains that meet a specific criteria. Domains are then purchased as a result of this search and tested. Of course, domain name registrars have an advantage here as they can taste domain names and return them within the 5-day refund period. As such, it costs them virtually nothing.
The average domainer simply cannot do this without custom developed research tools. Those that you can "buy off the shelf" on Internet web sites are simply not going to work effectively.
As more and more domain investors are using automated volume buying tools, the best domains are taken quickly. However, if you are creative with your keywords and criteria, you could still find a good deal.