I hatch all of my stock for the year before I start selling eggs. That way I know what the fertility rate is before I start shipping to people and I set randomly throughout the year to keep that in check. I send eggs out weekly and rarely have any problems. I send them in flat rate boxes so I can charge an even shipping amount all of the time. I do not replace eggs if there is a problem with shipping or hatching environment. Most of my eggs shipped people have reported as many as 9 out of 12 hatching. As long as they are packed good and fertile you should do OK. I charge $12 for 1 dozen and $14 for up to 3 dozen for shipping.