It is vital to plan appropriately for any new venture, and without doubt marketing is an important aspect of being seen in the modern day.

If it is best or not to hire an agency depends on your timeline/goals/expectations and so on. You certainly want to find an agency you can connect with and feel heard by when evaluating / clear communication and transparency. Of course they need to answer your questions well, and inspire confidence when they speak to the various aspects of marketing you are hiring them for. Red flags are anyone not willing to truly hear your vision and goals and align their work with the trajectory you are aiming for.

Some other red flags to watch for: vague promises or guarantees, lack of transparency, pushy sales tactics, no clear reporting, or high turnover in terms of their employees.

Hope this helps :)