Probably there is a solution of how to allow the installation of SQL toolbox and protect from mass usage at the same time? When I log in into Marketplace, I use my account and see the files that are available for my account. This is Independent of the project or domain and is tight to my user.
When you create a "hidden" Marketplace category containing SQL toolbox/Adminer and give the permission only for contributors, then no "simple, normal" (you know 😉 ) user would be able to install it. The contributor can log in into Marketplace from customers' AdminCP and install it though.
Then after investigating, purging, or whatever, the contributor deletes the app from the customer's installation. You can also add a big fat warning message in AdminCP with scary words that there is an app that can damage everything and the user should uninstall it immediately. Just in case, the developer forgets to delete it. 😉
This would protect the usage of the SQL toolbox or Adminer by the inexperienced user. But at the same time, allows a developer to debug.