Used vehicles: Pay GST on difference?

What's Madam trying to say? Buy at 12 Lakhs Sell at 9 Lakhs Pay GST on 3 Lakhs? Isn't 3 Lakhs a loss of value? What's the logic of GST on loss?

I thought we could claim depreciation on cars under income tax, if so cars are a "Capital Asset" how is GST applicable on sale of Capital Assets?