Query regarding Flipkart pickup charge and mixer exchange

Flipkart is taking 100 ₹ pick up charge and exchanging my old maharaja white line mixer @ 350. Total profit of 250. 

1. Now my question is that if due to some reason pickup boy reject exchange then I have to pay 250 or 350?
2. Any other website where I can sell my old mixer?
3. Any one who exchanged mixer grinder recently, please tell what they need as on filpkart nothing is written