As a young guy I worked for several “small” business. A mechanical contractor, a restaurant and a car wash. Every time I’d ask for a raise I’d get a sob story about tight margins ( “I under bid this project just to keep you guys working” blah blah blah ) and slowing business cycle etc. But ironically every year all of them would throw a nice catered summer bbq type get together. All them had nice houses, the kids drove new cars the wives had thick jewelry on. This is my first hand experience. 3 for 3 BS artists all.
1) Employer is not going to pay you more than he has to. Meaning, if he can find somebody to do the job equally well for less money, then you are replaced.
2) If your skills are such that some other employer would be willing to hire you away for more money, then you are going to say good bye unless he offers you what the market says you are worth. That's how you get a raise in real life.
3) If the job you are doing brings in less revenue than you are costing him, and he can't get anybody cheaper, then he's going to shut down that job. That might mean stopping to have a late shift, otherwise reducing business hours so that they're open just during peak times, or shutting down the business entirely.
A businessman creates a business so that HE can make money. Not for YOUR benefit. Paying you is only a means for him making money. Never forget that.