Thing to remember is this - if you're selling Puppy number 3, then you're selling Puppy number 3.
The timing of payment and the timing of delivery come after that.
By comparison, merely paying you take Puppy number 3 off the market,*
while the buyer decides if they actually want it, or can actually have it,
or while they keep shopping around... that is a different transaction.
Either way, in the case of the latter, there's no right to a refund for a change of (their) mind.
If however, you decide (say on animal welfare grounds) not to sell to them, then you would refund (in full).
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* As distinct from selling it, but not actually delivering it until it's "ready"
The timing of payment and the timing of delivery come after that.
By comparison, merely paying you take Puppy number 3 off the market,*
while the buyer decides if they actually want it, or can actually have it,
or while they keep shopping around... that is a different transaction.
Either way, in the case of the latter, there's no right to a refund for a change of (their) mind.
If however, you decide (say on animal welfare grounds) not to sell to them, then you would refund (in full).
--------------------------------------------------
* As distinct from selling it, but not actually delivering it until it's "ready"