I use a cheapie tuner to get me in the ballpark, then I depend on my ear to give me the fine-tuning I want. As I said, I'm an approximately equal temperament bloke (a decent compromise for melody-playing in different keys), though most harmonicas I've bought in that compromise tuning just need a couple of tweaked reeds per octave to keep me happy. If you choose to buy very cheap harmonicas, which abound, then you're beyond help...