I have a list of products, a list of sellers and the zipcode from the sellers. What I want to do is show the customer a list of products that can be delivery on their zipcode area.
First off, you'd have to have your customers log in or establish an account before browsing. Is that reasonable? If it is, then you have their zipcode.
Second, you have to then tag each product with a zipcode. That is easy. In Shopify you can use the built-in Metafields.
Now, in your Liquid, since you know the customer zipcode, and the product zipcodes are also available, you could show/hide specific products. For example, in a collection, when rendering the products, only render the ones where the zipcodes match. You need no Apps or special programming to pull this off. Just organize your products to have that zipcode and ensure your customers login before browsing.