Hi Patricia, thanks for asking. I'll quote (community manager) Enrique's previous forum posts:
Some candidates volunteer for the position (usually through the support system), some are recommended by current moderators or by other members, and others are selected by staff among site members.
Advice and feedback are asked from other moderators (sometimes personally, sometimes globally) but the ultimate decision and responsibility falls on site staff.
What moderators are and do is described here
The principles upon which ProZ.com has been built can be found in the document Sixteen (16) cornerstones of ProZ.com
All the candidates designated for site moderation are chosen based on the criteria stated in these documents.
I've also added the above to the FAQ.
By the way, I see a number of support tickets from you, but none was on this subject and all are closed. The best way to get an answer from site staff is to enter a support ticket.