This is exactly what sets B2B e-commerce apart from typical retail e-commerce. In B2B business relationships, almost every customer has different conditions: some have contract pricing, some have volume-based tiers, some can only view specific products.
A system designed specifically for B2B should allow you to set the catalog range, price tiers, and payment terms for each customer. When customers log in, they see their own version of the catalog and won't see other customers' prices. This way, when customers place self-service orders, they automatically receive the terms that have already been negotiated, and sales staff don't need to manually verify or send additional confirmation emails.
Once conditions are configured in the system, sales staff can automatically pull them in when creating orders, eliminating the need to look up contracts every time.