Anything I sell that could possibly need or benefit from them comes with a fact sheet/instructions. I even send processed chickens home with recipes.
It can't hurt to make up a little fact sheet on a note card that you can tuck inside your egg cartons in the future.
I would also put your terms and conditions on the reverse side of that card. If, under no circumstances, will you be willing to replace eggs or give special consideration make that well known. Unless it's in plain writing on the wall people, to some extent, tend to expect to be accommodated. It's human nature, I suppose.
Also keep in mind we all know your intentions were pure. We know you. The people he talks to know him, not you. They will know HIS story, which from the sounds of his level of frustration is that he got bum eggs from you. Stories are never one-sided, but one side is most anyone ever gets to hear on things like this. Unfortunate, but true.
How important is repeat and referral business to you? That, is what you have to ask yourself. If it won't break your heart if word gets around certain circles that is a tarnish to your rep. Don't worry about it. But if you are trying to build and at anytime in the future want to be a serious breeder/egg/chick seller in the local community, take that into consideration too.
Am I saying he's right? No. Am I saying he should be catered to again and again? Heck no! What I am saying is weight the cause and effect, the cost and gain/loss of your actions in this situation. And then decide what that means for you and where you want to be/go with this pursuit. We all have to draw our own lines in the sand, make our own boundaries. Think about it and you'll know what's right for you.
Personally, word of mouth has been the single most powerful catalyst I have had in any of my endeavors. I've seen it, I know how much it is worth -- how much it earns me, how much it saves me -- and as a result of that it's very, very important to me and I will go to great, GREAT lengths to make things "right" by the customer even if what happens is in no way my fault. I will not compromise my ethics or my welfare for it, but if making it right is a dozen free eggs or a few extra processed chickens? So be it.
Just my opinion of course. Good luck -- sometimes dealing with people is HARD!