Is there a way to lock down cards so members can't modify/add/archive or delete?

Question

I only want members to be able to view but not change anything

Arnau Martí · Answer

Yes, when you click to a member photo in the top of the board, you can see if you can make them ADMIN or NORMAL. So when you are Bussiness you can choose OBSERVER aswell.

Chelsea Peitz · Answer

If I upgrade to business acct and I already have members on a board, can I switch them to observers easily?

Arnau Martí · Answer

If you own a bussiness class acount you can add Observers to your board. 
With free or gold acount i think the only way is to do a public board. 
Keep in mind that public boards are scaned by google bots.