New students can be tricky. You want to believe that they will take a few lessons and become inspired to practice for an hour or more per day playing scales, Hannon and new pieces that they are working on, and in some cases, that is exactly what happens, but what if they quickly lose interest and decide that the piano is not for them? If you spent thousands on a piano or digital piano, you may find that you now have a nice looking piece of furniture, or that you have to sell for substantially less than you paid.
So you have to ask yourself, is this your idea for them to play, or is it theirs? Did you wake up today and decide that you are going to play piano, or have you played before and know the commitment level needed to improve?
If you are committed to having a piano in your house because you like the look, then go with something nice and that way you will still be happy if you or your child lose interest. If you are unsure, then go with a beginner digital piano or rent a digital piano and the money that you spend on the rental period will be much less than the loss you would take if you had to sell one you purchased. You will also be able to reassess and potentially upgrade to something that fits the style that the student has developed. You will be much more likely to make the right purchase if you have developed some playing skill and know what to look and listen for when you purchase the piano that you know you will keep.