Who you buy from
Updated
The supply side decides consistency, and consistency is what keeps wholesale accounts.
Four supply lines
Oils and butters. Lye. Fragrance and color. Packaging.
They behave differently: oils vary by crop and lot, lye is a commodity, fragrance is proprietary, packaging is a minimum-order problem.
Which means one purchasing approach across all four is wrong.
Oils
Buy food-grade or cosmetic-grade from a supplier who states the specification, and keep the lot number.
Fresh matters more than price: an oil close to the end of its life makes a bar that spots early, and you will blame the recipe.
Buy in a size you will use in a reasonable window rather than the size with the best unit price, which is the commonest way a small maker creates rancidity.
And note that a change of oil supplier changes the SAP value slightly, so the lye calculation should be rechecked rather than reused.
Lye
Sodium hydroxide of known purity, from a supplier who will provide a safety data sheet.
That sheet is not paperwork: it is where the handling, storage and first aid information comes from, and it is what an insurer or an inspector asks for.
Buy from a supplier used to shipping it, since it is a regulated shipment and a general retailer frequently cannot.
Store it dry, sealed and labeled, away from acids and away from anywhere it can be mistaken for something else.
Fragrance, and the question to ask
Ask every fragrance supplier three things: is it skin safe at your use rate, does it hold through cold process cure, and does it accelerate, discolor or rice.
Good suppliers answer all three and publish the usage rate.
Keep the documentation per lot, because a fragrance reformulated quietly is a common cause of a batch that suddenly seizes.
And buy a sample before a batch, always, because the cheapest test is one bar and the most expensive is forty.