How to "find an extremely well connected broker" and "work with a broker who genuinely specializes in that specific community"?

I often see posts like this one https://www.reddit.com/r/dubairealestate/comments/1vjpa2o/every_3rd_post_on_this_subreddit_is_now_a_right/

where the advice is:

"If you have time, you can buy off plan directly from the developer. In that case, find an extremely well connected broker who can secure you a good unit and a good deal.

If you want something ready, buy in the secondary market and work with a broker who genuinely specializes in that specific community."

This seems to be great advice - but how do you find a good broker when everyone claims to be? What are the statistics to look at?