First and foremost I hope this doesn’t discourage you from moving forward with building basses. I’ve been admiring your daphne blue jazz (but I already have two jazzes 😆). It’s bad luck to have a difficult customer experience out the gate.
What I get from your post is that you want the customer to have a nice buying experience but then not have buyers remorse! Maybe you offer one free service, to be redeemed within a year, with each instrument (adjusting selling price accordingly)? Or match whatever statutory obligation for returns/refunds is common? There’s a bit of a reassurance there rather than, for the buyer, this sense of slight anxiety that they’re buying something from a builder who, as yet, is “unproven” - despite what they may feel about the instrument in person on the day. Personally I need a bit of time to warm up to an instrument and decide whether it’s for me.
I think this echoes the point about selling a service, which may be far removed from your aim to enjoy
building basses and cover your costs.
If it were me I’d accept the instrument back irrespective of who’s right and wrong in the situation, offer a full refund, chalk it up to experience, and live to fight another day. Path of least resistance and all that, which may well be better for your heart, if not your wallet.