Brand new unused car seat from Mumzword, bought for 521

Children's car seat suitable for ages 0 to 6 years, brand new, I bought it a year ago for my daughter but never used it because my car is small. It has been stored with me all this time, I want to sell it because I am moving. I bought it from Mumzword for 500 and something, I want 300 for it since it is completely new