Lately, whenever I turn on the fan (not even the AC necessarily), a tangy smell like Elmer's School Glue or caulk comes out of the vents. The mechanics at Firestone don't recognize the smell.
Many salon workers face low wages, so tipping is their means of making ends meet. (And on that note, if you suspect your salon has poor conditions for its employees, report it to your local public advocate's office.) Tip 20% for a standard manicure, more if you feel your service was exceptional.
Tip discreetly, respectfully and from the full amount if you use a coupon or gift certificate to offset the bill. When in doubt, you're allowed to ask (preferably the receptionist or concierge, and not the person you'd actually be tipping) if tipping is customary and generally how much is appropriate.