When a recycler hauls your equipment for free, asks nothing about your data, holds no certifications, and offers no paperwork, the economics only work one way: resale. You're not the customer in that transaction — your equipment is the inventory, and whatever data is on it rides along.
The questions that separate certified vendors from drive flippers: NAID AAA certification with endorsements for your media types, R2v3 for the recycling and resale chain, serialized certificates as standard practice, documented chain of custody, and straight answers about downstream processing.
One document tells you almost everything: ask for a sample certificate of destruction before you sign anything. If it doesn't list serial numbers, you've learned what you needed to know.
Section 11 of the guide is a complete due-diligence question set — non-negotiables, differentiators, and red flags.