cheating by seller during GOSF

321603616393
The product was available for Rs 300 two days back . Now he has increased the price to 400 and is offering a 10% discount.
41 PCS TOOL KIT HOME, PC, Car, etc. Screwdriver Set Curatetools
10% DISCOUNT VOUCHER EBAY10DEAL - LIMITED TIME OFFER -321603616393

 

Where do I complain ? How do I warn innocent buyers