I love this. I also built a business like that[0]. It's super niche. I have maintained this small business for soon to be 13 years now. Most of what has worked has been maintaining great relationships with the few customers I have.
I think the most important thing for me have been offering amazing support. I always reply to all e-mails right away and make it my top priority giving them my best help.
Congratulations on your success, and best of luck going forward!
Congratulations on your success, and best of luck going forward!
[0] https://www.mino.no.