Supplement labels are dense, and much of the density is regulatory rather than informative. Here is the part that is actually worth your attention.
1. The serving size, before anything else
Every number on the panel is per serving. If one product’s serving is one capsule and another’s is three, their panels are not comparable until you have divided. This is the single most common way two products that look different are the same, and two that look the same are not.
2. The form, not just the name
Magnesium oxide and magnesium citrate are both "magnesium". Different forms of the same element behave differently in the gut. The form is usually printed right after the name, in smaller type.
3. Whether a blend is broken down
A "proprietary blend" gives a total weight for several ingredients without saying how much of each. It is legal and it is common. It also means you cannot tell whether the interesting ingredient is most of the blend or a trace.
If the amount of an ingredient is not stated, treat the ingredient as not stated.
4. The percentage of a reference intake
Where a percentage of a daily reference value is shown, it is calculated against a population reference, not against you. It is a useful scale, not a target.
5. What the certifications actually cover
Manufacturing certifications describe how a facility operates — hygiene, documentation, traceability. They are meaningful, and they say nothing about whether a product works. Those are separate questions and separate evidence.
6. The wording of the benefit
Careful phrasing tends to signal a careful company. Language that promises a specific outcome, or that describes a supplement as treating a condition, is a reason to look harder, not a reason to buy.