I honestly don't see the motivation for making any personal drama as public as this, it hurts the entire community... Why you have choosen to put this on the trending page is beyond me @kingscrown.
On a personal basis I do feel anyone offering a paid service like @booster should be able to deny certain costumers from participating. I look at this in the same way that a bar or nightclub can deny entrance to people that don't act in a way that is of interest to the venue.
That being said giving a downvote to someone paying for your services seems like a bad public way to act @fyrstikken. If you had refunded him directly and told him he was not welcome to use your service I would support your actions.
I would urge both of you to find a better place to have this kind of discussions then on the trending page of Steemit (if needed at all). When this kinda post is the first thing new users run into, there is a huge risk they won't choose to stay...
The trending page is full of crap anyways, why break that tradition?
I get where you are coming from, hopefully the upcoming communities feature will help sort content on this platform in a better way...
One thing that I've realized, is that a lot of time is spend and on personal drama here.