It's not recommended and your ability to sync regularly is severely limited in free Gmail and trial G Suite accounts, but here's a way that you can test out your Better Scheduling trial without a G Suite account... or use it this way forever! :)
In your Gmail account, create the new calendars (if required) that you would like to sync your WorkflowMax data to. Under my Calendars click the twisty on the right hand side of the My Calendars heading, then select Create New Calendar
Name the calendar what you wish, and share it with the person who's staff account you want to sync it with from WorkflowMax, in this example I'm sharing it with Contractor A
Click Create Calendar to save it.
Then go through the Better Scheduling setup video from this point but when you get to this step follow the instructions here.
1. Set your sync interval to 60 minutes (Important!) as this will ensure you aren't shut off by Google for 24hrs for going over the allowed usage on an @gmail account.
2. Set your sync schedule to only start before your workday starts and end slightly after your workday finishes, syncing data while you are not working necessarily wastes your limited server quota in a consumer @gmail account.
Now continue on and complete the set up