I once had a customer come back to me with the long sad face, because he put his peppers out in an unheated greenhouse in March and they died.
Talk about no warranty!
I did have some more plants with me though, and I gave him a few more to kill (or whatever) - not a full replacement but more of a token of my sympathy. And that is only because he bought so many in the first place, and his wife bought some other stuff from me too at a very slow market, I was happy enough to give him a freebie.
More usually, if people come telling that their plants died, you commiserate a little but never, never offer a replacement! They can buy one if they want it, and they often do.