That's the first and foremost thing I'll see. I can tell most insincere smiles - turn-offs. If sight of me displeases you, say so and we can depart amicably with a broken appt fee/tip for your time. Fake smiles bother me.  
Otherwise with smiles, I dislike when providers have just scarfed lunch and have food bits stuck in her teeth. As you can imagine, those smiles are either grotesque or hilarious depending on her choice of meal. I have to admit a fave memory was one where the lady (whom I saw regularly) blackened a couple of her teeth - after dolling herself to the nines - just to see my WTF look.

Other preferences about what a lady wears (other opinions may vary)
Clothing - what we discussed via email/phone (my fantasy) or something close to your ad/website pics (because your marketing photos work).
Perfume - light smell, if any. Bath & Body Works scents are fine too.
Make-up - light.
Jewelry - none.
Shoes - I'm not into shoes, but I dislike thick soled/hi-heel shoes. Flats work just fine. Height or lack thereof isn't a concern of mine.
Mani/Pedi - clean, groomed nails. I'm not into artwork on nails.

I can't think of what else a lady might wear when she opens the door. Hope this helps.

Kosh