I never went to flamenco shows in Granada but saw the places in the caves of Sacromonte . They look pretty authentic and since that area is merged with the gypsy area it should be authentic , However , Granada , like Sevilla is aimed at tourists . Don't be too put off by that as the shows can still be spectacular . MM will confirm that it's much better to see flamenco in a small venue where you are maybe the only non-Spaniard ( I can recommend one place in Madrid where that is almost guaranteed ! ) .
I went to one place in Sevilla with some American guys ( military ) .. It was OK but 100% tourists .. Quite a big place with a menu in about 7 different languages !
If you can find a smaller bar/club .. more intimate .. maybe just a bar de copas where there's no food .. just drinks and music and dance . Ask at your hotel or hostal . I hope that some board members may be able to suggest specific venues .
As for my secret little Madrid venue , I`m going to post details of it soon . It was a shame that I didn't get to go there with MM but we went to some amazing flamenco shows in Madrid . Next time i`m in Madrid , MM , let's go to that place I told you about .. near where I was living in Barrio Salamanca .. owned by a flamenco artist from Granada .. who sang at the end of the evening with a group of gypsy dancers who'd just done a show in a small theatre across the road . The whiskey was flowing ... I was with a Spanish guy ,, he lived just over the M30 motorway .. How both of us got home is a miracle !