There is a similar service I think its purse.io which buys you your amazon checklist for you with bitcoins and they provide a free escrow with some kickass deals.Are you targeting the users with the same service ? 70% don't look that bad though.
Erm, I'm pretty much offering the same service, but I've heard of Purse.io but never actually been on the site, but yeah I'll be offering 70% for now, perhaps lower in the future, but mhm, it's a fair discount and I just want to get rid of my balance tbh.