Amazon Business / ULINE Safety / Grainger marketplace — should distributors list there?

Selectively. Three patterns:

• Amazon Business — mandatory presence for any distributor with corporate-procurement buyers. Amazon Business is now where 60%+ of mid-market companies buy ad-hoc PPE. Magento → Amazon via channel manager (Channel Advisor, Codisto, Sellbrite) or direct SP-API. List your compliance-flagged + brand-authorized SKUs only; let Grainger fight on the commodity dust masks. Margin: 8–15% after FBA fees + Amazon 6–15% referral. Worth it for volume + brand visibility.
• ULINE Safety — ULINE is a closed catalog distributor, not a marketplace. They do not resell yours. Compete with them on customer-service depth, fit-test programs, and brand-portal access ULINE does not have.
• Grainger marketplace — Grainger does run a third-party seller program (KeepStock partners + some white-label arrangements). Hard to get into; high fees; not worth pursuing for distributors below $25M. Compete on direct e-commerce instead.
• Government channels (GSA, SEWP) — if you have GSA Schedule 84 (law enforcement, fire, rescue) or Schedule 70 (IT) plus a Section 8(a) / SDVOSB / WOSB certification, the federal market is huge. Magento can serve GSA via a separate B2B customer group with GSA-priced catalogs. Compliance overhead is real.

Channel mix I recommend for a typical $5M–$25M safety distributor: 60% own Magento store (corporate accounts + B2B), 20% Amazon Business, 10% other marketplaces (Walmart Business, eBay Industrial), 10% federal/state contracts. Single channel above 50% is a fragility risk — Amazon can suspend listings overnight on a compliance dispute.