Window spray damage, cost to replair

I bought a ps4 but it came with no hdmi so i couldnt test it and it was dodgy (the controller ) and i contacted the seller and he said to put window cleaner on it to make it work. Now it was turning and flashing lights and vibrating non stop and after 10 minutes it died and wont turn on. The scammer refused to give me a refund but after i threatend him to take him to court he losened up and offered me a £5 refund for repairs but im dont think it even costs that. What can i do abd how much does it actually cost in british poumds