Because there are so few NEW knitting machines available.
If you are looking to purchase a machine or add to your collection of machines, here are some questions to ask.
1What is the brand of the machine?
Japanese machines:
Brother and Knit King were made by the same manufacturer
Toyota is another common brand
Singer, Studio and Silver Reed also were made by the same manufacturer
Passap:
Passap machines are a different breed altogether. Most machine knitters either use Japanese machines or Passap, but many use both. Research the available gauges and base your decision on what type of knitting you want to do.
2 What is the gauge of the machine?
In other words, you are asking what weight of yarn would be appropriate. If the seller doesn't know, have them measure (in millimeters) the distance from the center of one needle to the center of the needle next to it. Needle Pitch
3How old is the machine?
Visit the MachineKnitting.com Knitting Machine Database to research models and the dates they were introduced. The most commonly available used machines were manufactured in the 70's, 80's and 90's. There are a few new machines being made today. One potential problem with a used machine is finding parts. Metal bed machines are workhorses. If it was cared for and not dropped, used machines need minimal parts
Looking for a brand new, fresh-out-of -the-box knitting machine?
4Has the machine been used for production knitting?
5Where has the machine been stored? Is there visible rust? How much was it used?
Rusty needles can be replaced, but check the needlebed itself for rust.
6What is included with the machine?
At a minimum there should be a needle bed with needles, the Cam (Carriage) (commonly 2 pieces), a Tension Mast , instruction manual, power cord (if it's an electronic machine), and hand tools.
7 Is the machine working?
If you are purchasing from a knitter, they should be able to demonstrate that the machine works with the parts being sold. Have them do a little knitting for you. Or ask for photos or videos of the machine in action
8 Is there an instruction manual?
Manuals are available online for many machines,Visit the Knit it Now manuals collection but it would be best to have the manual for the machine you are considering.
There are many machine knitting forums online with helpful knitters that can answer specific questions about machine brands and models.