How do you decide who comes in 1st, 2nd and 3rd in the Rancor Raid (when most can solo it)?

We play the 1 toon game. We typically designate a faction that all must use. We don't collect screenshot s and have had very few issues.
The only problem we had was people sending in their single toon really late, after some were already loaded for their solo run. This ensuredoes that they finished with the top score. After we put an end to that, it has been smooth sailing.