Puppy Milling
Puppy milling (in the context of Wajas.com) is when a user mass breeds their wajas to create a large number of pups. This isn't terribly common anymore, and the exact method and purpose for doing this can vary. The primary purpose currently seems to be to create large number of muddy wajas to sell for cheap (usually 50,000 WC and below) with the intention that OWFers will buy said wajas just to release them and get them off the market. If breeding high LQ wajas, a player can produce 3-4 pups per breeding. This makes it possible (though inefficient) to sell the pups for very cheap and still make a small profit on each pup.
A famous incident during which puppy milling became extremely common was the initial release of the Obsessed Waja Fan. During the early days of her release, she would pay a great deal for wajas that were higher generation and had high stats. Because of this, some users took advantage and bred tons of high stat, high gen wajas indiscriminately to send the resulting pups to her for a tremendous profit. The admins caught on to this shortly after the incident and removed the OWF to later re-release her in her current form (which pays a flat 10,000 WC for any waja rather than basing it on the waja's attributes).
Whatever the reason, puppy milling is frowned upon by the majority of the player base because it floods the market and takes a toll on the website's already dwindling server space. To discourage puppy milling by taking away the posibility of it generating a profit in a reasonable time frame, many OWFers will not buy wajas that are under 1000 days old (which is about three years).