This will be my second year selling seeds so I don't have much experience with this issue. I personally wouldn't ask for refund/replacement unless the seeds arrived mushy or what have you. There are way too many ways that people germinate seeds and too many variables to what may go wrong; you never know what they may have done to the seeds.
Example: I can't remember if it was on the Robin or one of the message boards but someone was told by another person to microwave the seeds to get them to germinate faster. I would have to say. IMHO, that microwaving would be the death of a seed.
I did have one person last year tell me that not one of the 70 seeds they got from me germinated. There were 4 different crosses and honestly I can't believe that not a single one germinated. This is a person that should know how to do seeds, but you never know. Everyone else had good germination rates from the seeds.
What I did was offer to replace them this fall after I remade the cross this season and they were fine with it.
My personal opinion is replace the seeds if you can, if you don't have more of that cross offer them something similar. If they want the exact cross offer to replace them when you make the cross again. I would also ask them how long they had been planted (since some seeds can take quite awhile to germinate) and how they germinated/planted them and such to see what may have gone wrong. Maybe they are new (maybe not) and had no clue as to what they were doing or haven't waited long enough.
