non-exclusive - everyone can be a customer (unlike consulting or SEO)
easy for prospect to understand
most business owners value a good reputation
easy to deliver
recurring (at least for a while)
Should be a long term strategy.
Good data to support the value
Very little competition
Hard for prospects to price shop
The best prospects probably would be businesses you wouldn't want to work with. There's probably a good reason they have a bad reputation.
Its a new service business owners aren't familiar with.
Hard to measure roi.
Easy for businesses to do in-house