well your lfs knows very little, motoro's aren't small rays and easily exceed 2 foot in diameter, they would be too big even for a 6 foot tank, and as simonas stated 2 foot isn't really suitable for any rays, except maybe potamotrygon scobina, which you won't find easily anyway and not for less than a few hundred pounds each. you might ge away with a single potamotrygon reticulatus in a 6x2x2 but nothing more than one and nothing smaller than 6x2x2.
do not get a motoro, they are big rays and would need something like at least 6x3x2.
i wouldn't advise you to buy any ray for some time, i spent at least a couple of years researching them and still i consider myself very much still learning, if you knew the slightest about rays you'd of known your lfs was tanking rubbish. take your time in research, its not fair on the fish to keep them crampt and they will suffer and die very quickly.