Good afternoon, lolang, 

I appreciate you turning to the Community for support. 

When it comes to transitioning a client from QuickBooks Desktop to QuickBooks Online, only you can decided if you'd like to charge a fee for the time and effort you put into it. However, I will leave this post open for other Community members to share their experiences.

we're here, if any other questions come to mind.

@lolang 

This will depend on the year version of QB Desktop your client is using. If your client is using an outdated version, you will need to upgrade the file (or purchase a 3rd party service to do so) before converting it to QB Online.

Hi lolang,

To have a better understanding of the migration process, you can review our Comprehensive Guide to moving data to QuickBooks Online.

I hope you find this to be helpful!