I think I would....not walk....away from that breeder!!! The first breeder I met with told me the heart issues were "blown out of proportion to scare people and weren't that big of a deal". Needless to say, after that comment I thanked her for her time and left. I wasn't comfortable arguing the point because I was not very informed at the time. Now....she would have gotten an earful from me!!
Anyway who denies sm or mvd is a problem is trying to pull the wool over someone's eyes. Do not deal with them. If you have problems down the line this is not someone who is going to stand by you and support you.
Loving mom to Jake, Shelby and Micah