I would demand the information as it is common practice in other parts of the country.
There is not much you can do about it,exept make the highest possible offer you can make and hope for the best, the listing agent can not tell you how much the other offer is.Good luck
But in today's market terms and conditions have more weight than price. There are also unethical Realtors who will use another Realtor's offer to better their own clients position should they have a buyer on line for the property they have listed, or there may be no other offer and they are trying to up yours to a better price. Anything is possible in Miami. Look ,if the property is meant to be yours, you'll get it, if not, there is plenty of inventory out there, so don't feel bad.