I bought a really helpful book the other day by Ego Iwegbu-Daley who has had nail bars in Selfridges and Top Shop among others. It helps guide you through the process of planning and launching a nail bar. It was quite pricey but the advice is so specialised that it is worth it. Anyway, she says that one of the cons of taking on self-employed nail techs is that even if the salon gets busier and busier the rental you receive remains the same -this is quite a draw back that I had not fully appreciated.