You can trade any resource for any other on a one-to-one (or low-to-low) base. For example I request one niter for one horse. If I want 20 niter I just need to repeat this 20 times. The trading partner though won’t give me 20 niter for 20 horses in one step because he thinks I’ll get too much advantage of such deal (which is fine so far...) but then he shouldn’t give away the next niter in this low amount for the next time (same turn). This makes the resource management meaningless since you can almost always get any amount of resource with zero effort especially if you have many allies. Furthermore I can trade late era resources like aluminum for like two luxury resources which is too generous, eliminates all amenity problems. Both problems point to a possible bug where resources when traded in low amounts are treated as in before GS where resources were not accumulative (counted as one like luxuries).