If you want to sell a product on your website, but only want to allow it to be picked up in your store, you can enable the "In-Store Sale Only" pref in the product edit window. To do this, search for the product on your Inventory > Products page. Click on the "Edit" button under the product, and check the box for "In-Store Sale Only". Then save.
Having this enabled will make it so customers can only select an "In-Store Pickup" shipping option at checkout. The customer will still have access to all normal forms of payment that you accept.
Important information for 3rd Party Sales Channels (TCGPlayer & Amazon):
It will also prevent the item from further syncing with Amazon or TCGPlayer. However it will not desync the item from 3rd party sales channels. This means you will need to check the box for "in-store sale only" before adding any quantities.
If you have any existing quantities in stock and you check the box for "in-store sale only", those quantities will remain on TCGPlayer and Amazon. However, the sync will be broken, so those sales channels will not receive any further quantity or price updates from you. To properly enable "in-store sale only" on products that already have quantity synced, follow these steps:
Set the quantity to 0 and save.
Wait for the quantity to sync to the sales channel, so that you no longer have a listing active there.
Check the box for "in-store sale only" and save the product.
Re-add the quantity to the product.