As far as ABX goes, there's nothing useful imo. But being presented with something different to what I'm used to may very well be. Going sideways isn't useful either but a stark contrast/improvement in transient performance or bottom end control is telling. If that's the case, you can probably expect better imaging and resolution as well.
However to answer the op, I would say firstly you need a reference to make an educated opinion. That reference is just that, your experience. It takes experience to establish your own understanding of the descriptors used in defining sq. Being told what to listen for without having something to compare to is not helpful. As I mentioned in another thread, I had a stunning wake up call when after shrugging in wonder about what the big deal is, the salesman directed me to "listen to the cymbals", "listen to the snare", listen to the bass definition. I had brought back a NAD receiver I was not pleased with and they gave me full return credit for something else. The something else being that stark contrast. If it wasn't, I would have simply traded for something different, but likely not better. I'm not interested in changes I have to agonize over to recognize. That's just useless. You may need a mentor, but if it's not sideways you'll hear it during an audition, good or bad.