Is there a way to make this safe for both sides
Unfortunately you will run the risk of ending up as a mule for scammers and crackers, whitewashing their dirty IBAN transfers into untraceable BTC.
I don't see a simple solution unless you involve out of band communication like a registered letter from the bank account owner, signing the agreement to send you the money and get BTC in return.
But this would introduce huge delays that would scare potential customers.
