Just wanted to open up some feedback for the new feature we deployed today: Store managers! See the blog post here, play around with the feature, and let us know if you have any questions.
Looking forward to hearing from you!
"Uploading" items requires the user to have access to your actual Second Life account and log into the account in the Viewer since the items are "uploaded" through your own Inventory.
Giving others, including people you might trust to be a Store Manager, access to your Second Life account is a huge security and privacy risk and is also a violation of the Terms of Service.