Case study exams - I presume you're talking about the Section 4 Essay in the HSC exam. Regardless, this also stays true for any assignments/other exams.
You're gonna want to structure your essays around different topics/talking points. Say, if you're talking about financial sources regarding debt and equity, talk about BOTH businesses in that paragraph. Same goes with any topics relevant to both businesses. This way, you're not repeating information later down e.g. "Paragraph 1: Business A satisfies its financial needs through...." then "Paragraph 2: Business B satisfies its financial needs through...." it just looks clunky if you repeat the same stuff in different paragraphs. This also applies to most case studies in any subject.
As well, you're gonna want to highlight differences between the two business. The main things you may hear is "find a business that is doing well and then another one that isn't doing well" or something like that. It's kind of true, kind of false. If both business are doing the same thing in the same way with the same outcome, don't talk about it, or at least don't repeat it. Just say "Business A does....Business B also does this with the same effect/degree of effectiveness." Differences can be in effectiveness, e.g. "Business A used equity financing through...which was successful/effective because...But Business B also used (same form of equity financing) but was not successful/effective because..."
Always make sure you make some degree of judgement. Say it is effective, or successful, or wasn't effective, ineffective, effective to a limited extent, etc. It makes your essay look better than if you just say "Business A's decision to use (this) negatively impacted the business".
Always start your paragraphs out with a bit of theory THEN go into case studies for detailed examples of how this (positively or negatively) impacted the business. e.g. "When deciding on how to satisfy financial needs, businesses have the option to use debt and equity financing. The main forms of debt are...equity are..." then give examples on the main forms (short term debt + examples, long term debt + examples) with the examples going into more detail/describing the examples with pros/cons e.g. "Commercial bills have a variable lifetime of usually between 30-180 days, are often for larger amounts over $100k, are paid at the end of term, and rolled over with interest until they are paid in full. This lessens the impact of amount and interest repayments on cash flow, however may represent a significant leakage of funds at the end of term and can impact a business's financial position if a business is not prepared." THEN you have to make sure your examples are relevant to the theory you have just stated. So, make sure you have examples of which businesses use which form (e.g. Business A has high gearing, meaning high debt, leading to higher risk). Don't introduce main examples of debt/equity financing (or irrelevant topics/examples/aspects of theory) if your businesses don't use it e.g. don't talk about commercial bills just to say Business A uses unsecured notes, which you didn't describe.
Always make sure you answer the question, memorise your syllabus. Your syllabus will directly dictate your points/topics you include in your essay. Don't memorise essays, memorise the syllabus in its entirety, then embellish/bullshit/expand upon those syllabus headings relevant to the question.
And, regarding hypothetical/made-up case studies, you won't get marked down for them. Sure, it may look good to use Qantas, but those are more stats you have to remember in combination with quotes. If you want to use real life ones, sure, go for it, but I find it easier to just make up case studies. In the end, your case studies have to support your points/topics/arguments and the theory you outlined in relation to the question.
Sorry for the long post, hope it helped. Sorry it's a bit late.