What’s the difference between seller and vendor used as defined terms for party names?
Here’s what Bryan Garner has to say in Garner’s Dictionary of Legal Usage:
In specific contexts, however, a differentiation is emerging: in computer contracting, the practice is to use vendor rather than seller almost exclusively. The term vendor is used in two senses: (1) “any member of the entire class of business entities (often the manufacturers or producers) engaged in marketing the particular product that a prospective purchaser may be interested in acquiring”; and (2) “the individual business entity that makes the ultimate sale (including a lease).” In computer contracting, vending and selling represent two distinct phases of commerce: vending emphasizes the process of engaging in marketing or offering a product for sale rather than the sale itself, while selling focuses on the final step in the process—the actual sale.
I think that makes heavy weather of it. Here’s my distinction: Use vendor for a party that’s in the business of selling the property in question; use seller for a party that isn’t.
Don’t dream of using vendee instead of buyer. Besides inviting –or/-ee confusion, no humanoid says vendee.
What about supplier? Use supplier for a party that not only is in the business of selling widgets but is contracting with you to supply you widgets over time.