This common mistake can tank a salary negotiation in minutes, says hiring expert: ‘It looks like a cash grab'

The secret to a successful salary negotiation isn't what you ask for, but how you do it. 

Whether you want 10%, 20% or 50% more than what was offered, you need to make a compelling case for why you're worth it. 

Adam Broda, a senior manager at Amazon and career coach, has spent more than a decade in the hiring field — and he says one of the most common and costly mistakes people make in a salary negotiation is asking for a higher salary without explaining the rationale behind their request.

"If you're just throwing out numbers without providing a chain of logic as to how you got there, it looks like a cash grab," he tells CNBC Make It. 

You also run the risk of coming across as "inauthentic or selfish," Broda cautions. 

"It has the potential to cast a more negative impression on your potential boss," he says. "If I don't understand why you need that money or why it's important to you, it can look like you're asking for more because you thought you could take advantage of the hiring team." 

Explaining why you deserve a higher salary makes the conversation more collaborative than confrontational. It also shows the hiring manager that you're invested in the role and have done your homework, Broda adds.

For example: You might ask for an additional $10,000 to help offset the cost of a longer commute, or so the pay better aligns with the market average of the role. 

DON'T MISS: The ultimate guide to negotiating a higher salary

Broda recommends providing one or two solid examples of why the company should invest more in you, and to be as specific as possible. 

You might bring up: 

• Years of experience, if you have more than the employer stated as a minimum requirement
• Results you've achieved in previous roles, including revenue you've helped generate
• Skills you possess that are in high demand within your field

Referencing estimated salaries in comparable roles, or other industry data, to support your ask is a strong play, Broda says. 

When employers see data supporting your request, it becomes clear that you're looking for a fair deal rather than an over-the-top increase. This data-driven approach helps hiring managers justify any increases on their end, too.

Payscale, LinkedIn, ZipRecruiter and other websites offer free databases showing the pay for different roles in a wide range of industries. You can also talk to people in your network and get their perspectives on the company, the current salary trends in the market and your talent. 

Ultimately, "hiring managers are on your side in salary negotiations," says Broda. "We want people to be excited to join our company and feel good about the offer they're getting. The more information we have in a negotiation, the better we can advocate for you."

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