Selling it as soon as you've bought it — Chinese expression
The most common way you would say is


  现学现卖 or 现炒现卖


However, the actual and original expression is


  旋炒旋卖


if you read ancient Chinese novels. The character 旋 means right after. This expression is more correct, I would say.

However, you would just say 现学现卖 or 现炒现卖 nowadays, if you were to use the original expression, most likely people would not understand.