No way of telling what kind of hatch rate you will get. My first time ever hatching shipped eggs I ordered a dozen and the seller sent 15 and I hatched 11 healthy chicks, but honestly I've never done that well percentage wise since with shipped eggs. (Lots of times you do get extras but with this seller only having only one hen, maybe not). I would be mildly concerned with age of eggs and the assumption that her hen will lay every day straight but it may still work out. Is there something special about this particular seller like a very close location or a hard to find breed? Otherwise, I think I might be tempted to order from someone with a few more hens both for fresher eggs and the possibility of a few extras. I also would wonder if only one hen means someone who has little experience shipping eggs? A good experienced packer can help hatching rates. But in the end, it is pretty much luck of the draw. I wouldn't count on all 4 hatching and I would figure out what you are going to do if you only get one chick. Heck, that happened to me a couple of years ago with a dozen eggs. My cat got wild and knocked the incubator off the table and I lost everything but one. I had a broody (when you have a bunch of silkies, you pretty much always have a broody) and I stuck him under the mom and he was happy. But without a mom, raising one chick by himself is problematic. Will you use a broody, get a friend chick from the feed store or elsewhere locally, or whatever? It is something to think about.