I have been trying out various breeds of sheep in my spinning; this typically involves shopping online as some of the more "obscure" breeds (the meat/wool ones common in North America) aren't available from my LYS.
I usually buy roving or combed tops, and that is usually commercially prepared. Commercially combed fiber is usually of pretty good quality.
However, recently I ended up with this, from a source I had not used before:
It is kind of hard to see, but there are a whole bunch of little nebs - "balls" or "pills" - in this roving. You can see them in the pointy tail most clearly. The roving is full of them. There are too many to pick out, and I don't have tools to fix this (if it is possible to fix - I don't know enough about preparation to judge). This is a fairly fine fiber (polypay sheep) and I had wanted to test it for socks. However, with this kind of pilling, it is basically impossible to spin fine. Every time you hit one of those nebs, you will end up with a blob in your single:
Lesson: you need very well-prepared roving for fine spinning.
I'm rather disappointed in this roving and I will have to let the shop know that they have ruined their fleece by improperly carding it. While I don't know very much about carding, I am guessing that what happened here was that the carding machine is too coarse for the fiber, which leads to excessive pilling.
I can still use the singles - I've made a 4-ply worsted weight yarn out of it, the multiple plies "even out" the issues - but you cannot make socks with this kind of stuff. So it's not a total loss!
**update** I've learned more in the time since I wrote this post: nebs can occur not only by carding on too coarse a cloth (the little needles are too fat or too far apart), but may also be caused by weak fiber. Carding or combing weak fiber causes it to break, which creates the nebs or pills.