Hi and welcome to YT.
You are wise to be uncertain about this puppy. Sounds like a broker or 'greeder' to me. 7 weeks is much too young to be away from its momma and in some States it is illegal to sell a pup under 8 weeks. The colors do not sound like a properly bred Yorkie to the standard. It is good the pup was sold and I hope you will find a pup from a reputable breeder. Then you will get a healthy and well sociallized dog with a health guarantee. Hope someone here can help you find the baby you are looking for.