I see your point, but that's not necessarily the case. You can cancel right after taking the test without knowing your score (say you had an off day, were ill on day of exam, etc). So you're right that they can and may assume you did badly, but there are other reasons people cancel, too, and they may look upon a cancelled score a little less critically than they would a bad score.
Yep, or just using old PTs. I was initially devastated when I went from mid 160s to high 150s when I started using the newer PTs. It only took a few weeks of getting used to them though, and I was back in the mid-low 160s (ended up with a 162).