[Note: Some have suggested the total overhead paid to SB is only 5% after cancellation. The chips cost SB .078BTC each - he charged .086BTC, but is only refunding .081BTC. Sure looks like 15% to me.]
10% of .078 = 0.0078 <-- SB's markup
0.078 + 0.0078 = 0.0858 <-- cost per chip from SB rounded up to .086
95% of 0.086 = 0.0817 <-- refund from SB as stated in the email and on forums
100% - 95% = 5% <-- markup lost in the course of doing business. seriously. this happens. check the thread for evidence of work being done.
May I suggest
https://www.khanacademy.org/ for your remedial maths
Exactly.. Anger and a will to write it out loud is clouding some peoples judgements.. Even him taking the full 9.9% i would agree on.
However, he is not the best communicator and he should have someone working on the forums, which is his ONLY point of sales.