It's not my main source of income but I take side jobs of installing a wordpress + customizing it to their requirements.
There are people that build entire companies using WordPress as a base @kaisrmaulo5, exactly like you are talking about. Within WordPress there is probably enough business to make an entire business from just one WordPress concentration. Though my entire business is not WordPress I do have aspects of WordPress in my overall business offering.
As to where you can sell your services and wares, it would depend on the product or offering. For services there are of course websites like Upwork but I'd probably have a different suggestion if you were concentrated on just selling plugins and yet another if you were just selling templates. Ultimately I'd suggest looking around and experimenting on what works best for you. There will certainly be websites you like better than others.
roy darling *my posts seem a lot shorter in my head
I am using Wordpress on my blog but I am running it as a passive income source. I am a full-time professional making good from my job but Wordpress gives me an additional source of income.