Although it is very difficult for an agency to gauge how the campaigns will perform without any previous data. Still try and get a rough commitment from them on KPI’s they will deliver on and timelines that they plan to adhere to. For instance 4-8 months is a good timeline for SEO to work and start reaching the first page in most cases unless you are in a highly competitive market.
These are a few points that you can keep in mind while picking a digital marketing company to outsource your work. Let us know they helped and also if you know any more tips.