So much depends on the field of work.
In a professional field I'd expect an idea of the salary range upfront. I'm really not interested in spending time researching a company and interviewing for a job only to find the salary is a joke. It's all very well saying it's "competitive" but that doesn't actually mean anything useful.
At the other end of the scale I remember seeing a vacancy posted that made it very clear the applicant would receive the National Minimum Wage. In other words, we're paying you the absolute minimum we're legally allowed to pay you. Don't forget to take pride in your work.
The kind of contract that offers zero base hours with anything you actually work being extra probably doesn't work for a lot of people but if all you want is a bit of extra pocket money it could be quite convenient to have an income, albeit sporadic, that you can pick up and put down as it suits you.