To the seller, the order types are called “listing types”.
The order types affect the seller’s experience when they post a new listing. When a seller creates a new listing they first choose which category they list in (if you have more than one category), and then which order type to be used. If you have enabled multiple order types for the category the seller chose, he or she needs to choose one of them when posting a new listing.
If you have enabled the price field the seller needs to add a price to their listing. If you have enabled online transactions the seller need to fill out their payment details to receive money.