The thing is, the customer is automatically a piece of shit for even contacting the store owner to begin with. It's like calling to say "Hey, I bought some flowers but they died yesterday because I didn't give them water"... Okay? And? Cool story bro? Try some personal responsibility next time?
OP sounds like they are doing the right thing, it's just fucking sad that that is what we have come to as a society. The fact that OP has to literally pay money for other people's mistakes just to avoid drama, yelp reviews, and bitchy annoying customers.
Dude you have no idea how many times a year I have to go through this routine with customers. They always come in with a chip on their shoulder and claim the flowers I sold them must have some type of disease. After 15 years it's easy to tell it was just a lack of water but every damn time the customer digs in and refuses to admit they just didn't water their plants....sigh....it gets really tiring.
It's actually an interesting study in generational sociology. Boomers are by far the worst. They always storm in and demand a refund or replacement but when told there is not a warranty or replacement for the plants they killed 99% of the time they ALWAYS make a scene are rude and storm out and most of the time leave a negative review online.
Gen Xers and Millennial's are a little different. They either call or ask through social media but rarely come in person. When told that there is no warranty or replacement on the plant they killed they generally tend to be more understanding and leave it be. Occasionally they leave a poor or negative review online but not very often.
Anyway, just an interesting observation I've had over the past 15 years of being a business owner/horticulturalist. There are many other observations too. One that always makes me chuckle is how differently most men and women perceive plants. Men are always about vegetables, turf(grass/lawn), and foliage plants such as Coleus and women are all about the blooming flowers like petunias, geraniums, and impatiens. There is always some overlap but mostly it follows along those lines.