I just purchased the premium version of Repair Buddy and an interesting thing that I noticed is that the premium version has the same plugin slug("computer-repair-shop") as the free version of the plugin as found on https://wordpress.org/plugins/computer-repair-shop/
Which made me curious as to how updates through the WordPress dashboard would work(since WordPress would naturally want to install updates from WordPress.org). So I went ahead and I did a comparison between the two versions and I'm afraid I didn't see anything that would tell WordPress to download updates from your site(you can see the different files below - only large_invoice.php has a significant difference between free and premium).
I'm hoping that you plan on adding code in the premium version that will pull updates from your end and not WordPress.org. Perhaps you might need to add some sort of licensing keys for the premium version so that people can't just download the premium version for free if the know the URL :)
And just to summarise - my concern here is that when you release a new version on WordPress.org in some time and I update the plugin on my site through the WordPress dashboard, I'll get the free version installed and not the premium version. So then I'd have to go manually download the premium version and install it again - which is less than ideal :)
Thank you for your time,