You can email seller or call directly if he or she leaves his or her tel no. You should also check if a seller is a frequenter (that means he or she may make a living or try to make some money from selling piano), if that is the case, ignore him or her (you can check by click "view poster's other ad" on the right side corner, or even google it)
Some sellers are moving or just want to sell their pianos for more space because their kids have grown up and left houses; some sellers who live in a nice areas may sell a good piano for changes, but you need to move quickly before "professional piano buyer" moves in
Also remeber that moving a piano costs roughly $200 ~ 300 in Ottawa plus about 100~200 tuning