I once went in to buy a Blues Harp from a music shop. Picked out the one I wanted and asked the man if I could try it first. He said no, not allowed but I'll use this little bellows on it. I explained that this tells me very little as some notes take more air than others and you need to feel that. He said sorry still not allowed. I said OK then as I'm in to buy an instrument anyway what if I buy it, try it in front of you and if I'm not happy you take it back and give me another one. He said OK then. I bought it, tried it, explained and showed him that a couple of notes were taking too much air. He gave me another one, put the original 'back in the box and back on the shelf'!   ???