Many employers try to count employees as salary to get more work out of them without paying overtime. This is illegal. There are rules in place already, it’s not just up to the employer to decide.
First, let’s clarify that salary means exempt from overtime, so you’ll see it referred to as exempt (salary) vs non-exempt (hourly with overtime).
In order to be exempt/salary, the employee needs to either be a true manager or have a white-collar job. A shift manager is not a true manager if they don’t make hiring and firing decisions, have control over what is done, how it’s done and who does it, etc. White-collar jobs are learned professions meaning they (usually) require a college degree and advanced skills.
It’s amazing that even in accounting I’ve seen management tell employees they’re exempt because they manage their clients. Well, no they don’t. Not if they don’t have the power to refuse a client, fire a client, or control how much the client pays. Depending on what all their duties are, they MAY be exempt because accounting can qualify as a white-collar profession. But even that doesn’t apply if the employee’s duties are very limited and controlled by management. For example, someone running payroll, reports, deciding and entering journal entries, paying the clients’ bills, handling their accounts receivable, reconciling the bank accounts, etc. may be exempt. But an employee who only does data entry or accounts receivable has no control and those jobs don’t require a college degree or advanced skills, you can train an inexperienced person to do those tasks.
So again, the guidelines are relatively clear and it is not just up to the employer. Here is a link to what the FLSA says about exempt vs non–exempt. Again, if you’re still unsure, I’m happy to try to help and give you my non-lawyer answer (or tell you that you need to ask an attorney in this case).