Vertical pianos, normally placed against or near walls, don't interact with hard floor surfaces as intimately as do grands. However, if your vertical is in the middle of a very "live" space, such as a dance studio or theater rehearsal room, it can benefit from some sort of floor covering under it that extends a few feet out from the piano on all sides. If a vertical's sound is still too resonant or bright, whether the piano is up against a wall or out in the middle of the room, you can eliminate some of this by hanging a heavy fabric cover or blanket over the back of the instrument. Not very stylish, but it works.
Some high-end piano dealers will give you time to audition an instrument in your home or studio before you make a final commitment to purchase. I strongly recommend taking advantage of any such offer — the room in which you place your piano is as important as the instrument itself in determining the ultimate sound.
Lewis Lipnick is the principal contrabassoonist of the National Symphony Orchestra in Washington, DC, and an internationally-acclaimed soloist and teacher. His consulting firm, LipnickDesign, specializes in designing high-resolution audio and video systems, recording studios, and home theaters; in environmental sound control; and in the acoustical design of commercial and residential spaces. Visit his website at www.lipnickdesign.com.