I bought a tunic a while ago, but (a) as I only offer spray tanning I didn't want to look like I was trying to look like a beauty therapist when I'm not, if you know what I mean, and (b) doing lots of spray tans at one time can involve lots of bending and stretching and being comfortable is very important to me(!), so I compromised with my company-embroidered polo shirts.
However, I've used a few mobile and home-based beauty therapists and I've come to expect them to be wearing some kind of tunic or similar (although I don't think it would particularly put me off if they didn't wear a tunic).