Two quotes for the same diaphragm can differ by a third and still cost you the same money — or the cheaper one can end up dearer once it is standing in your warehouse. The number that decides is not the unit price. It is what the unit price includes, and what happens to the shipment after it leaves the supplier.
Four things are worth settling in writing before a first order.
1. Which Incoterm the price includes
A price with no Incoterm is not a price. The three you will meet most often:
- EXW — the goods are yours at the supplier's door. Loading, inland transport, export clearance, freight and insurance are all on you. The lowest headline figure, and the one that hides the most.
- FOB — the supplier gets the goods cleared and loaded at the named port. You take over from there. For sea freight this is the common middle ground.
- CIF — freight and insurance to your port are in the price. Convenient, and it means the supplier chose the carrier and the cover, not you.
None of them is the right one in general. EXW suits a buyer with a freight forwarder they trust; CIF suits a first shipment where you would rather not arrange anything. What matters is that both sides mean the same thing by the number, and that the named port or address is written out. We quote EXW or FOB Istanbul and arrange CIF on request, which is a sentence worth getting in writing from any supplier, not just from us.
2. Which documents travel with the goods
Ask, before you order, exactly which documents the supplier will issue: commercial invoice, packing list, and whatever origin document your customs authority expects. Türkiye has preferential trade arrangements with several regions, and the paperwork that unlocks a lower duty rate is issued at shipment — not afterwards, when you have discovered you needed it.
This is a question with a factual answer. If a supplier is vague about it, that is information about the supplier.
3. How payment is staged
For a first order with a supplier you have not worked with, advance payment by T/T is the normal arrangement in this trade, and an L/C at sight is the usual alternative once volumes justify the bank charges. Neither is unusual and neither should be treated as a red flag.
What should be treated as a red flag: any request to send part of the money to a third party — a "shipping agent", a "customs facilitator", an account in a different name from the company you are buying from. A legitimate supplier invoices you from the entity you contracted with, to an account in that entity's name. If the account name and the company name do not match, stop and ask why before you transfer anything.
4. The part numbers, in writing
Most disputes we hear about are not about quality. They are about two parties meaning different parts.
Write the numbers into the order: Type, stroke, and the OEM number you cross-referenced from. "Type 24 long stroke, replacing WABCO 897 120 536 4" leaves nothing to interpret. "T24 diaphragms" leaves the stroke open, and normal and long stroke are different parts that will not substitute for each other.
If you started from a number on a chamber, our cross-reference gets you to the Type and stroke; the size chart shows the whole range on one page. Put the result in the purchase order rather than in a chat message.
Before the first order, ask for samples
A sample settles in a week what documents argue about for a month. We send up to ten pieces free of charge and you cover the shipping — the details are on the free sample page. Fit one. A part that seats correctly and seals is a better reference than any certificate, and we do not hold certifications that would substitute for that test.
The short version
Ask any supplier, including us, these four questions before the first purchase order:
- Which Incoterm, to which named port or address?
- Which documents will ship with the goods?
- What are the payment terms, and to which account in whose name?
- Exactly which part, by Type, stroke and OEM number?
Four answers, one email. They will not make a bad supplier good, but they will show you which kind you are dealing with — and the good ones answer all four without hesitating.