You need to understand how easy to use it will be for you to manage moving forwards. Will you be able to edit your website content yourself, or will it be complicated so even minor changes require the help of a designer?
Another factor to consider is what happens in the future if you want to move to a new supplier. Is the platform transferrable between different website hosts, or is it a fully hosted service that can’t be moved?
More questions that lead on from this one:
Is the platform regularly updated?
Is it secure?
What features does it offer?
Is it SEO friendly?
Make sure you fully understand the solution you are looking at. As your business advances, will your platform advance with you, or will you need to start over again?