I'm open to suggestions.
I suggest you just sell your keys at a fair price, and same price for everybody no matter the rank.
Of cause you escrow if the buyer is newbee.
After that you sell some more keys, then sell some more keys or other goods.
Then will you slowly and honestly gain a reputations, previous buyers will vouch for you and perhaps buy again, and new buyers can see that you are an honest trader.
You are not going to fool anybody here with "buying" trust, anybody on default trust will never leave you positive feedback, neutral at most.
When that is said, then will I wish you good luck with building your business, my gut feeling say you have honest intentions.