I started in a new job a few months ago, and it is quite niche and unique as I have never seen a similar role advertised. Usually the work I do in my role would be done by another kind of role alongside their other responsibilities, but they have hired me to just focus on that set of tasks alone (if that makes sense). As such, there is no 'industry average' of salary, and I can only compare it to my previous role where I worked on a wider variety of tasks but in less depth, whereas this is a narrower focus but in a lot more detail/depth.
In cases like this, how would it be determined if an employer is paying you enough, given that there is nothing else to compare it too?