If he add more then 10 person then admin/sript will choose the candidate randomly. Seems theymos had edited OP with new updates.
It's not random, imo. If it was random, theymos would not say "whom your vote will be most useful."
Each user's number of "votes" in the last two criteria will be limited to floor(earned_merit / (10 or 250, depending on the criteria)). If you trust more people than your limit, then you will vote for the people to whom your vote will be the most useful, more-or-less.
I think it will be choosen by either the members trust score or whom most of the people have included.
For example, if someone has 20 earned merits and includes 3 member in trust list, system will check among those 3 member who has been included by most others person. Assume, I have 20 earned merit and included A, B, C in my trust list. Anyone from this 3 will be excluded by-
Assume-
A- trusted by 20 members
B- trusted by 11 members
C- trusted by 15 members.
Then my vote will go for A and C, B will be excluded.
Is that correct, can someone confirm?