yes I spend ages going through music shops in my free time when I'm not on assignment! I love flutes (or did when I played) and so it was just fun to discover a flute maker making flutes. The hardest thing about buying dizi flutes is ... not being able to read chinese. I can't tell the brand names etc, but I recognise some of the qualities in the way they are made - for example - the type of bamboo; how it is built; the shape of the embouchure hole; the cut of the holes, and the pitch of the notes across the octaves.
If a dizi is hard to blow, it may need adjustment to the dimo membrane, or to the head cork, or to the tuning tenon which can be stretched. Most will not have as much resistance as professional Boehm silver flutes - the more resistance, the more 'colour' the flute is usually capable of, but then, it is not a 'freeblowing flute' which is easier for a beginner. Now - if you use plastic sellotape in the dimo hole, you will muffle the sound, and you will not get the vibration required to make the dizi sound - it will sound flat and uninvolving. The di mo paper is really cheap - just get some of the er jiao (glue) which rubs into little water to adhere it.
I have a D,C, G, F dizi as well as a few xiao flutes! I hand picked them all during my travels