Please don't be wooed by words like "market value" or "competitive". Know your worth and hold to it!
(Before I continue, what I'm about to say may not be news to many, but I've had this revelation firsthand from behind the scenes, and I want to share it for people my age who are working or looking for jobs and may not have considered it. What I'm about to say is also based on the hypothetical assumption that a job-seeker has the experience, skills, and qualifications to warrant a salary that's reflective of what they bring to the table. Know that this is purely based on observation and not personal grievance.)
When hiring personnel mention "market value", they're not talking about how much you or what you can do are actually worth. I venture to say that what they're really referring to is how much (or how little) they can pay you in comparison to other companies who hire people to do similar work. Their goal is to get the most quality work out of you for the lowest possible price, so when hiring personnel or job ads mention "competitive rates" or "competitive salaries", please do not read too much into it. "Competitive" doesn't mean that what they offer you is all that you should get or that there isn't any money to pay you more. It means that their rates/salaries are in line with (maybe a few dollars more than) the precedent that they and other companies have been able to set for the same type of work. And in too many cases, people with the requisite skills and experience or worth more than that precedent.
And I understand, this is business and businesses have budgets to maintain. I understand that even if people are underpaid, it doesn't necessarily follow that their employers don't value their contributions at least in theory; they might get acknowledged in other ways. I also understand that not everyone is in a position to hold out for something else that will pay more, especially if the offer presented to them is the only viable option they have. Money is money and people gotta eat. But I've learned quite a few lessons working in recruitment so far, and one of the most important is that market value (what people are willing to pay you) and your worth are not synonymous. They should be, and in various instances I'm sure they are depending on the field and the position that someone is aiming for, but they often are not.
I'm increasingly of the mind that worth cannot be completely measured in a conventional sense anyway. However, to the extent that it can be measured quantitatively and compensated monetarily, you have to be incredibly self-aware and know what you will and won't accept. Drake and many people before and after him have implored folks to "Know yourself, know your worth", and as someone who helps hire people I'm begging you not to take this advice lightly. Do what you gotta do, but don't ever let anyone make you second-guess what you have to offer.