Glasgow Central - Dumfries - Carlisle Scotrail services were meant to have an on-board catering trolley service from April 2017 as per the Franchise agreement. It hasn't happened, which is not surprising given the financial difficulties Abellio seem to be experiencing lately.
Im sure they used to along with Stranraer . Im sure Stranraer services use to have seat reservations . Scotrail would need to base catering staff at central though .
If Edinburgh to Glasgow via Falkirk High has catering then why dosent via shotts !