I could not find any way to list "services" in Shopify POS or products and DEAR POS does not support it yet (September 13 2017).
However, you can create a "Quick Sale" (Not a new item it won't work) in Shopify POS and process a transaction.
It will then become listed in DEAR as a service.
You can edit that service, add it to the category you whish for exemple or map it to a particular revenue account.
Then if you re-use the EXACT SAME NAME again it will re-use the same service.
You can use it in :
+ DEAR invoices
+ Shopify DRAFT (Use EXACT SAME NAME IN "Add custom item")
+ Shopify POS (USE THE EXACT SAME NAME IN QUICK SALE)
But can I mix services and products this way? YES, Services and products will be imported in the proper section of each invoices imported from Shopify to DEAR.
I would recommand to keep a list of "CODENAME" for your services in your cash drawer so clerck can use them properly.
Definitly not the easiest way but it's working.