When ask this question, as a rule of thumb, I look at two criteria; how old is your practice, and what type of alloys are you installing.
If your practice is 10 years old or older, it's likely some of the work you are extracting, is work you’ve previously installed. So, depending on the alloys you are using, i.e. non-precious, semi-precious, noble, or high noble, then your scrap will follow suit, for the most part.
So, if you are installing mostly non-precious, well you can expect a large portion of your scrap will test non-precious...thus driving your payout down. On the other hand, if you’re installing semi or precious alloys, then you can expect your scrap to be better in general.