All good advice above. The point is, the heights of both truck and trailer vary. Many WDH's have adjustment for different heights for that reason.
Approximate height is good enough to tow it home at low speeds. However, mounting the WDH and adjusting height and load are part of picking up a new TT for the first time. Take tools and allow time to make adjustments.
Get approximate height from the seller. Just call and ask.
I wish you good luck and happy trails ahead!