That is, when asked why I am looking for another job?
The commonly-used challenge or more variety reason is true and I can't really say it's because the current job sucks.
How do I know when/if it's okay to say it's because I want to earn a better salary??
I wish I had said this in a recent interview, it would have been more honest.
"I am looking for an opportunity that is paying closer to Market rates for my Position and experience."
Or alternatively "I don't feel I'm being adequately compensated for the value that I am generating"
It's perfectly to say that in an interview AS LONG as you back it up with some arguments: what's the value that you bring to the party, what is the "market rate" for your skill set, how are you planning to contributed to the bottom line, etc.
Everybody wants more money: the trick is to justify it in a reasonable way.
Most people realise you work for money so there's no need to be too coy about that aspect.
It's fine to say you are looking for more money*. So long as you are within budget "you pay more that I am getting for the same job" is a perfectly good reason. If you can refer to market rate that's your inroad - "Your position pays what I am looking for". If pressed you can say you are currently under market with no way of fixing it if you stay.
That said, if you are uncomfortable just coming out with it, other softer reasons might be hours, commute, flex, WFH or something if you want to deflect without drawing attention to the actual salary.
Other ways are to invoke progression options (if that's what you want or prepared to accept). "I am senior X qualified but where I am there are no senior roles on the horizon". "I've outgrown the role but there's no way forward to X so I have to move on to achieve that" etc. Salary is a by-product of those things but you can state your goal in a less blatant $ chasing way if it's basically true.
Another way it is to put a bit of spin on what they offer. For example, if you can judge the major job functions from the position description or during an interview, you can refer to that, e.g. "I am currently doing a lot of X but really enjoy Y much more. This opportunity seems to have much more Y than where I am now and I would be excited to contribute more in that area".
Pros of all the above are that they are honest and legitimate answers. If the company has a budget and prepared to pay the right candidate, there's no downside. Cons are only really if the employer is trying to screw you and they don't care.
In all cases, it basically has to be true, otherwise you're just getting a short term win that will wear off quickly.
*Where I am - might not apply to other places, such as USA as far as I can tell.
What's the pros and cons of saying I want a better salary?
The Pros are : If your talents and experiences truly deserve a better salary, the potential employer may give you a higher salary.
However, the potential employer may attempt to negotiate with you if their budget is limited. So, it may take some time to negotiate.
The Cons are: If your talents and experiences don't really deserve a better salary, then the potential employer may reject your application right away, and choose another candidate. If they already pick another candidate, then you can't ask them to go back and hire you with their original offer.
However, if the employer have a difficult time finding another candidate, they may attempt to negotiate with you. So, it may take some time to negotiate.
I can't really say it's because the current job sucks.
It's true. You should not say negative things about your current job, boss, coworkers, or company. Never say negative things like those in an interview because the interviewers may not have good impressions about you.
How do I know when/if it's okay to say it's because I want to earn a better salary??
The best way to earn a better salary is to provide good justifications to potential employers.
First, you need to do serious research on the web to find out what a person with similar skills and experiences as yours earn in the city that the company is located (if this is an onsite and not a remote position).
A fair salary depends on the skills, experiences of the candidates, and location of the companies as the cost of livings varies from one city to another.
There are many websites such as Glass Door, etc... that provides this salary info.
Then, when you go to an interview, you should be able to provide a professional, precise, and factual argument as to why you deserve a better salary based on your skills and experience (in a specific market/city). Again, you should be able to back up your argument with your research on the web.
Pros:
Cons:
While honesty is usually the best policy. It really isn't in this case. Employers expect you to lie to them as to why you want to work for them. It makes them feel nice and fuzzy inside, like you are really there because you want to. Being honest about your reason shines a light on that social lie... And makes prospective employers feel uncomfortable, because you are assaulting the fabric lies of societal convention*. Making people uncomfortable makes them not want to hire you.
TLDR: Bad idea, don't do it. Every field has an accepted lie that people use.. "I am looking to grow as a <name of the profession> is fairly standard. It is better if you include a plausible way that you could grow at your new job (that doesn't include money, but implies that you are going to be making more money).. Such as taking the lead on a project, opportunities to mentor younger engineers, etc... This phrase is kind of equivalent to "I tripped" from middle school. Everyone knows that its really because of money, but know states it outright so the societal lie that people come to work because they enjoy work is preserved.*
* I know this doesn't apply everywhere... For example, I make about 1/2 of what I could if I were to work elsewhere. But I a) really like my co-workers/boss. b) spend about 1/20th of what I would on housing about 1/2 of what I would on basic necessities if I were to were to move to area's with a higher paying job. So my net income after expenses/tax is significantly higher..
PRO If you want more money, there is no CON to asking for the salary you would like to get when interviewing for a new position.
CON None
HOWEVER If your "real" answer is current job sucks, then asking for higher salary is not the answer, it's a deflection. Why does current job suck? You must be brutally honest when you answer that for yourself. Then, you dress up that brutal answer with a professional, judiciously worded statement when interviewing for the new job.
Some brief examples (based on personal experience):
