With an Airtable form, you can prevent items from showing up in a linked record field based on a view in your base, so you can setup a view in your base that only shows in-stock items. But an Airtable form wouldn’t be able to do math — for example, calculating if the quantity that the person wants exceeds what you have in stock. You also can’t display how many items are left in stock with an Airtable form.
I would probably recommend using Fillout’s advanced forms for Airtable for the sort of functionality that you’re looking for, because you can pull in data from your Airtable base into your forms (such as lookup fields, rollup fields, formula fields, attachment fields),, and you can also perform live math calculations on your forms as well.
Then, you can conditionally hide things on your form based on that math.
I can’t specifically tell you off the top of my head how to design the form in Fillout, but they have really fantastic tech support and they should be able to help.
— ScottWorld, Expert Airtable Consultants