I have had one of my dogs shipped to me. It went fine---BUT I wouldn't do it again if there were no other alternative. I think that the process is very stressful for the pup---and the potential of the pup getting lost is scary. 
Also, like someone mentioned---if the breeder is USDA licensed---I don't think that is a good sign...isn't it a sign of a puppymill? I could be wrong, but I think that I heard that somewhere. Puppymills are prevelent in MO. 
You may not want to spend the money on a quality breeder (typically a pet yorkie goes for about $1200 i think)---but that money can save you on medical cost and heartbreak.  
puppymillrescue Home Page has some info on puppymills. 
I think that everyone here has offered you sound advice and I hope that you will be open minded and consider it. They only want what is best for you. 
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 Chrissy, Izze (Yorkshire Terrier),Molly & Suzie (Toy Poodles), Chachi (Chihuahua)