Hi Sreeram,
You are right, the criteria field in Audience Performance Report only gives the values as specified in the Criteria prefixes section of
this guide. The CriterionUserList will be displayed in the format boomuserlist:123456. To get the details of the user list, you will need to use the
AdwordsUserListService and retrieve the object where the id matches the number following "boomuserlist:". If you are having trouble locating the userlist, could you please point me to the specific entry in your report that you are trying to look up along with your CID? You can use reply privately to author while responding. As I said in my previous response, you will get the Criteria (Audience) in the form "uservertical::". You can check the correspondent value for this criteria in
In-Market categories guide. Let me know if you have any further questions.