BPs and products are shared across all companies. There are no existing field to link them to a company so what you are demanding is a customization. And this is on purpose for consolidations, inter-co we need to have the same data used across different companies, so I recommend you to keep this logic.

Keep in mind, if a product managed in stock has no product-site you won't be able to managed it on the missing sites. On the BP record (on the last tab), you can define the list of company that can work with the BP.

Anyway, I know there might be good reasons to do such a customization then the simpliest way would be to create a specific field to create a link between a company and a BP / product. Then you can use this field to setup low level restrictions.

The pain points will be: how do you manage a customer or a supplier or an item that is shared between at least 2 companies?

BPs and products are shared across all companies. There are no existing field to link them to a company so what you are demanding is a customization. And this is on purpose for consolidations, inter-co we need to have the same data used across different companies, so I recommend you to keep this logic.

Keep in mind, if a product managed in stock has no product-site you won't be able to managed it on the missing sites. On the BP record (on the last tab), you can define the list of company that can work with the BP.

Anyway, I know there might be good reasons to do such a customization then the simpliest way would be to create a specific field to create a link between a company and a BP / product. Then you can use this field to setup low level restrictions.

The pain points will be: how do you manage a customer or a supplier or an item that is shared between at least 2 companies?

Hi, Just to add on what Julien was saying. You can find Row Level Permission under "Setup -> Users -> Row Level Permissions", and tie the permission to the user under the organization tab of "Setup -> Users -> Users", but as Julien mentioned, you will need to be able to identify the company it belongs to on the product record for this work. 

And to keep the standard, you can use restricted price structure to avoid saling some products for some companies.