What kind of serum to buy?

I'm curious, could you please elaborate on the specific type of serum that one should consider purchasing? Are there certain factors that should be taken into account, such as the intended purpose, brand reputation, or even the ingredients? Is there a particular serum that has proven to be more effective than others in the market? Additionally, how important is it to consult a professional before making a decision about which serum to buy? I'm eager to learn more about the best practices when it comes to selecting the right serum for my needs.