How to compare two quotes that look the same

A practice gets two quotes. One is meaningfully cheaper. The obvious conclusion is usually the wrong one, because the two documents are not describing the same transaction — they are describing the same noun, which is not the same thing.

Normalise the unit first

Before anything else, establish that both quotes describe the same quantity of the same thing. Vial size differs. Concentration differs. For vesicle preparations, the quoted particle count differs — and a count is only comparable when both suppliers name the method used to measure it. Two numbers produced by different analytical methods are not two measurements of the same property.

Then price the things the quote does not mention

• Shipping conditions. Cryopreserved material needs a validated shipper, dry ice, and somebody physically present to receive it. That cost exists whether or not it appears on the quote.
• Storage. If one option requires −80°C and you do not have it, the quote is not cheaper — it is a capital expenditure with a consumable attached.
• Preparation time. Staff minutes on the day are real cost. Lyophilized material has to be reconstituted; a pre-filled format does not.
• Wastage. Vial size that does not match your typical case produces remainder you pay for and discard.
• Minimum order and lead time. Capital tied up in inventory is a cost, and so is a case you cannot schedule.

Then price the thing that has no line item

What documentation arrives, and does it refer to the lot you received. A supplier who ships a specimen certificate rather than a lot-specific one has saved themselves a step and moved a risk onto you. It will cost nothing at all until the day somebody asks you what you injected and on what basis you believed it, and on that day it will be the only question.

The cheaper quote is often cheaper because something has been left out. The work is finding out what, before it turns out to be the part you needed.

A note on the opposite mistake

Expensive is not a proxy for careful. Price in this category is set by positioning at least as much as by cost, and there are suppliers charging a premium for exactly the documentation a cheaper competitor also provides. The point of the exercise is not to pick the dearest option; it is to make the two quotes describe the same transaction so the comparison means something.

Build the comparison as a table with a row for every item above, and make both suppliers fill it in. The one that resists the exercise has answered a question you did not have to ask.