Make your solution ubiquitous by making it easy to use.
This is the Coca-Cola lesson: be in an arms length of desire. Some service providers make it really difficult to use them. And then there are others — like Payfast — who make it really really easy to use their services (and so become the default solution — and deservedly, I hope, make lots of money).
If you want to start an commerce business there are two key services that you need for your site: a payment gateway and, if you're selling physical goods, a courier service which enables live delivery estimates.
Payfast is absolutely brilliant. You will find an easy to install plugin for whatever ecommerce platform you choose to use (I've tested Zencart, Opencart, Prestashop and Shopify). Payfast, I assume, totally dominate the online ecommerce payment environment in South Africa.
The plugin is free. As, cleverly, they've worked out that making it easier for you to install and use their service will deliver more revenue (they take a cut on payments).
The opposite of this is the courier service Fastway (we use them). There is no plugin for Fastway and they make it difficult for a normal person to install one (we've purchased a plugin for our Opencart platform). They don't provide a plugin (instead they have an API which then requires registration as well as a developer which costs you money).
What's more you can only contact the local franchisee (less one!). Totally useless.
BTW, Shopify is not much better. You have to pay a high monthly fee to use a courier service plugin.
So what are we doing? We are actively looking for another courier service which has a plugin for our ecommerce site (or at least testing one).