If you go to Setting-> General, you will see the Product Permissions toggle and it would allow you to set particular product permissions for specific user or users. This feature can be implemented in addition to the User Permissions and please see the details below:

If this toggle is turned to On, a new additional Editor Restriction section will appear under the User Permissions for each each user in the Profile tab. That section would allow to select a particular custom field, that would contain certain values, that only the admin can and needs to fill in first and set for each user in order to restrict some users from editing particular items or group of items and see the screenshot below:

For example if there are users, that should be working only with items of a particular Brand and no other users should to be able to edit those listings, except for the users that need to, then you can select Brand as a restriction field for all of the users. If the value Nike is added in that Brand field for user1 and Adidas for user2, then each user would be able to edit only the products and listings, that match the Brand values set in their restriction fields:

This is only one example of how this feature can be utilized, another example would to be to use a custom field like Office Location or Department and this would allow only the particular users from specific office or department to be able to edit the related products / listings and restrict other users from editing them. 

Please note that the field is case sensitive, so if you want your user to only update items with Brand of Adidas, you will need to make sure the Brand field is always filled in as "Adidas" capitalized properly. Having "adidas" in there as a value instead of "Adidas" can still have the item disabled for that user. 

If you might need any additional details or suggestions about this feature, please log a support ticket and we would be more than happy to help further with more information.