No, it's not all socialization! Genetics definitely are the bigger piece if the puzzle IMO. Good socialization and training can bring out the best in the dog, but ultimately you can only do so much with what you're given genetically.
Honestly, it can be tough, because some qualities come out as the dog hits maturity.
My suggestion would be to look for a repeat breeding, and look at the offspring from the previous litter, unless you know your bloodlines really well.
ETA: would they consider adopting? Then you know exactly what you're getting. Win/win