Just finding the leads that are most willing/interested in the service.
Currently I am going off - most recent review, # of reviews and an avg less than 3.0
bonus if the business has a website or any online pressence.
as far as industry type I am really going for whatever, hotels, dentists, retail, entertainment, etc.. any business I can find.
The process is also a little tedious, but I understand a single letter could potentially have a large payout, and some of these business it's crazy how poorly they are reviewed, some even have the courage to yell back at the reviewers, its insane to read haha.
Listen to 1337WuLF, I think people focus too much on low ratings & reviews from Yelp. Instead, just get in touch with as many businesses as possible