Preliminaries:

• Shopkeepers version: idk, I don't own the server, I'm just doing an suggestion
• Spigot version: again, I don't own the server, so I can't do /version

• I have checked that my issue/question does not get answered by:
  • The documentation.
  • The FAQ.
  • The Known Issues.
• I have checked all open and closed issues, but none seems to fit my issue/question.

Reproduction on a fresh and up-to-date Spigot server:

I was not able to reproduce my issue on a freshly setup and up-to-date Spigot server (currently idk what Spigot version) with Shopkeepers (currently again idk), with no other plugins and with no kinds of other server or client mods.

The issue:

Provide a detailed description of your problem and add as much information as possible which could help reproducing the issue.

Include:

• Description of the issue.
  I am making a shop with a friend but I can't open my friend's shopkeeper's chest (neither can he open mine)
• Step-by-step instructions on how to reproduce the issue.
  just.... using it.... and making a shop with a friend
• Observed behavior.
  I can't open his shopkeeper's chest
• Expected behavior.
  Actually expect the same as observed
• If items with special attributes are involved: Include instructions on how to create those items.
  none
• Server logs (from server startup until issue). Consider enabling debug mode in the config for additional console output.
  idk I don't have access to that
• If modified from default: Plugin configurations.
  probably not?
• .. Anything else that might be useful to reproduce and identify the issue.
  it's just a suggestion for a command to add other people to a shopkeeper

Duplicate of: #342
There are still some open questions regarding this feature in the linked ticket. Maybe consider posting your ideas on those there. Especially: Does your friend need to be able to edit the shop (trades, mob attributes, shop name, removal permission), or would chest access be sufficient for your usecase?