Yes def see how the litter is raised. The breeder hopefully would have a room full of ribbons and trophies from showing.
If I were to ever purchase another puppy, it would have to be from a breeder who breeds for the betterment of the breed, who breeds to akc standard, and that has won awards to prove it.
Anyway, check the health guarantee, it should not be just for one year, or for "life threatening" diseases only. For example, LP is not life threatening, but is passed on genetically, so a dog with this condition should not be bred. If the condition shows up, what will the breeder do about it?
They should sell only on a spay/neuter contract or limited registration. No reputable breeder will sell you a dog with full breeding rights unless you have known them for a long time and trust you with their line and all the hard work they've done for years and years.
Run away from anyone who uses marketable words like tea cup, baby doll face, teddy bear, hello kitty face (yes I'm serious), micro, etc, or anyone who breeds "designer dogs" morkies, and such. Or prices by size, the smaller the more expensive. Don't buy from anyone who is a one trait breeder, like only breeding for size, or for rare colors that are actually a fault and should not be priced higher. They should be breeding to meet the standard and preserve the yorkie "look". That's all I can think of right now.