I don’t see any issue with having such a feature so that authors who wanted this could utilize it.
My only concern would be setting up reasonable expectations for what is involved. Timeframe? What exactly “installation” includes? For example, “installation” to an author is a pretty straightforward process; “installation” to a customer might mean “set up my home page, add a menu, set up my slider”
I’ve had a variety of customers come to me upset that they paid for “installation services” for my plugin through Envato, because the Envato Studio freelancer that did the job simply uploaded the plugin and clicked “activate”, but didn’t do any configuration. I think customers probably expect a lot more than basic installation when paying for a service like that. I’m not saying that’s fair or unfair, just that we need to better manage expectations.