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In that scheme, the first thing I’d be worried about is the IRS. By that I mean making sure that you’ve got everything well aligned for them in case it became necessary at some point, and the fact that you will be making a bunch of purchase orders from your bank account. The Zelle account seems to tie to a bank and or visa/mastercard debit card, so you will have a bunch of inputs there to justify. All of this subject to the amounts you move around I figure (i.e. small amounts are probably not an issue, but bigger figures would likely need a proper justification – at least prepared just in case).
As to the fraud, I cannot discern if there is any loophole there. You’ll have to see if the money they send you to your Zelle account is always committed, or can be rolled-back for some reason as can happen with Paypal. The ultimate thing to watch out for is not sending BTCs if the received money is not absolutely solid.
Edit: First and foremost, ask yourself why you would get 10% for being a middle man providing no added value, when the straight forward method followed by most does not entail going through the process described in the OP. You are the legal face in these scheme, and that risk needs to be very clearly assessed.
