Using a third party tool like Dropbox, Sugarsync, etc., to sync directories is never a good idea when working with databases, particularly when the database records are complex, as with Garage Sale that uses financial information. You are 100% reliant on these tools to sync entire databases of files while making sure you don’t have the applications open and that you are not reading or writing to the database during the process. Syncing doesn’t always work properly and it becomes easy to corrupt database files or end up with mismatched files that contain different information.
Properly written programs that sync data examine individual things like time stamps for each record prior to syncing and they check each record for consistency and integrity before and after the syncing process to make sure you end up with the information you are expecting.
If this was a database of a personal DVD or CD collection it would be one thing, but the financial implications of messing with databases that are financial could be very problematic. I don’t recommend it.