Engage with their customers
Sell and manage product/service deliveries
Target specific customer audience
Show products/services availability
Whatsapp could be the right solution not facebook apps.
Also a combination of Yelp and Facebook/Whatsapp could lead replacing small business websites(I'm not telling that no smb website should exist) that going to make a fortune. The platform needs to accomplish these three things :
The ability to list core info like contact details, hours of operation, and service offerings in a minimalist fashion.
The ability to solicit feedback (not ratings) from customers in a low-friction, high-upside way.
An ad system that let's a 60 year-old luddite set up a campaign in less than 3 minutes without having to call anyone.
There's a lot to tell but I'll leave you with these thoughts.