On the admin interface, admins are able to manually add users they know they trust to e.g. trust_level_2.
When inviting new users, admins are able to select groups but not trust levels. This is a problem since those trusted people who are being invited are now being treated as new users who are prevented from doing various things, which is especially confusing when they interact via email and get errors like this:
Reason: Sorry, new users can only mention 2 users in a post. Sorry, new users can't put images in posts. Sorry, new users can only put 2 links in a post. If you can correct the problem, please try again.
I see there is discussion elsewhere about this issue of trust levels and invitations, but my case is more specific - methinks admins should be able to specify the trust level directly.