IMO you are only attracting scammers here. No reputable members here will trade with you. I a bit doubt you are holding that much btc. Could you sign an message from the holding address?
I am afraid but I must agree. 20% mark-up over the current price is just too much. Legit members will find some other way to buy that's lot cheaper.
I know you must protect yourself OP from the chargebacks with these 20% but I don't know if you will get anywhere with this plan!