if you are worried about the fiat value of a payment you receive then you have to discuss it with the sender before the payment is sent. you can come up with an agreement about the price and the cases where it has a sudden change but remember that it can cut both ways for example if you were paid when price was $10k and price went up to $13k then you will have to pay back the excess fiat that you received! $3000 per bitcoin!
depending on the size of the payment, the agreement can be a simple verbal one for small amounts or if it is large it can be a legal contract. it needs to address where you get the price from, the time frame the transaction has to be confirmed and the price change percentage that would require extra actions.
but others are correct, you are receiving bitcoin not fiat so you shouldn't even be concerned about fiat value of it. 1BTC is equal to 1BTC regardless of its price.
Ha ha ha, you are a very funny man, whereon earth is this done, how can he return the extra because he got higher dollar value, it was bitcoin that rewarded him for using its payment system to receive payment,, and he has no business with the payer, if the value had dropped as against the increase op talked about, would the sender had balanced him up if they have certain dollar amount they agreed on?
What if he decided to keep the coin in the wallet for 10 years, and within those 10 years, the value grows to give him like $10000 extra, are you saying he will still have to send it back to sender? I don’t think this is a wise idea, no matter the contract signed, the sender did not over pay, he paid him exactly what he needed to pay him, and that is his own luck if it grows higher.
