This is an old one, and I feel like it can often times be overlooked and seen as outdated and unprofitable. To this day I STILL use snail mail. There are a few key strategies that I implement and have a pretty damn high success rate with. ALWAYS have a clear and concise call to action with your potential clients that you are mailing. In terms of ORM, take screenshots of the businesses negative reviews and write on them with a red marker. Highly negative parts of the reviews, give feedback, show them exactly how others are seeing their business being represented online.
Make them realize that these reviews are actually costing them money every month. A lot of businesses that I have worked with ended up generating over thousands of dollars after only 1-2 months of online reputation management that they previously had been losing based on negative reputation. Also, make sure and hand address each individual letter. Business owners receive so much junk mail that is preaddressed and most times won't even bother opening it. Whenever you receive mail that is hand addressed you are more likely to open it. If any of this information actually helps anyone then great, let me know if you would like to know any more. Thanks and I wish you all success in your future marketing endeavors.