HA looks good

econ/exchange.py

@@ -125,8 +125,12 @@ class Exchange():
         Returns an order if the order is active. Returns None if submit has failed.
         """
         # calculate price for complete order fullfilment
+        prev=amount
         amount=int(amount)
-        full_price=round(price*amount,2)
+        if amount<1:
+            # invalid order
+            return None
+        full_price=round(price*amount)
 
 
         # Move resources into escrow