Mob sales can be done simply: From the menu on the left, go to Mobs> Touch the relevant mob to expand> Select Sell Mob > Enter details> Save. Mobs can also be selected from the map.
This information is then stored within a neat sales summary. You can find the sales summary by going to:
1. Menu (the three little lines in the top left of screen)
Note: If you're selling a mob that hasn't been added to a property yet, you will have to add that Mob to a paddock before it can be sold in Mobble