Wholesale pricing is rarely one size fits all. You can give any customer their own price on any variant without touching your list prices.
Setting a custom price
Open Customers and select the account.
Find the pricing section and choose the variant you want to override.
Enter the price this customer should pay.
Save.
From then on, that buyer sees your price for everything else and their negotiated price on that variant. You can set one override per variant per customer.
How it applies to orders
Prices resolve when an order line is created: if a custom price exists for that customer and variant, it's used; otherwise the variant's list price is. Once an order is placed, the price is frozen onto it — later changes to either the list price or the override never rewrite a placed order.
Live carts work the other way round: they always reflect current pricing, so a customer with items sitting in their cart will see a new price take effect before they check out.
Custom delivery and pickup rates
You can override delivery pricing the same way. On the customer's page, override a specific delivery method's weight tiers to give that buyer different rates — one override per method per customer. Useful when a customer is on your route anyway, or is far enough out to warrant a surcharge.
Tips
Overrides are invisible to other customers — nobody sees anyone else's pricing.
To move a customer back to list price, remove the override rather than setting it equal to the list price. That way future list-price changes carry through automatically.
Doing a broad price increase? Update list prices first, then review your overrides — they don't move on their own.