Hello Michael.
What do you mean by "sell solutions/apps"? Made in OutSystems?
If you develop them in your Personal Environment, clients won't be able to install them in their infrastructure (IPP).
What you can do is
1) work as a freelancer in companies and specialize in building a particular type of app. Practice makes perfect.
2) create your own site and sell Software as a Service.
If the apps you are selling are not OutSystems forget everything above.
You can create all types of Customer portals. Take a look at this case study.
If the work is too much for you/your team, of course you can hire OutSystems or other companies to build it for you. Or you can use an existing Costumer Services product instead of building your own.