he or she, of course, will give you good suggestion if you have no idea about it. This is the best way. Or if you cannot find that kind of person, do some research on the Internet, there will be lots of recommendations of second-hand piano that you can take them.
Buying a new one is not worthy in my opinion even if it is cheap because you even don’t know your daughter like it or not. Of course, you can get a new one if you have no problem with the money. For me, playing piano is always a happy thing because I have one with me. For the little kids, spends on how you guide them. Just remember to find a professional people to help you when you decide to buy a new one or an old one. Hope it helps.
