How Much Money Is On My Burton Gift Card I Have A Gift Voucher Worth £25 I Want To Sell For £15 As I Need The Money,where Would I Be Best Selling Them

I have a gift voucher worth £25 i want to sell for £15 as i need the money,where would i be best selling them - how much money is on my burton gift card

No expiration date on the heel, which are used in Top Shop, Top Man can, Burton, Miss Selfridge, Wallis, Dorothy Perkins, Evans, Outfit.
Was a gift from a friend, and he is really genuine watermark etc.Iam little money folowing only Christmas.
Everyone's ideas would be welcome, thank you.