This guide contains some points about purchasing High Street Gift Vouchers.
Recentely High Street Gift Vouchers did a recall on all the old style High Street Gift Vouchers as a security measure and the old style vouchers are no longer accepted by retailers.
The old style voucher has the list of retailers in a block and looks like this:
The new style vouchers will have the retailer's logos in a heart shape.
I have seen some people selling the old style voucher on Ebay and some people aren't using an image of the voucher so my advice is to ask the seller to provide a scan or photo of the voucher they're selling.
If you need more information on the recall of High Street Vouchers then please visit the High Street Gift Vouchers website.