i think what the OP is trying to say

if Mastercard usually had a 2% fee. and somehow someone hacked a retail terminal to charge 300% fee
EG $6.70 transaction with a $15.70 transaction fee.
comparable to
6.7btc tx out with 15.7btc fee
https://blockchain.info/tx/6fe69404e6c12b25b60fcd56cc6dc9fb169b24608943def6dbe1eb0a9388ed08

now knowing the retailer cant amend this issue as they never received the funds and the funds are alreadygone and its visa that received the fee (bitcoin mining pool received)
there shouldnt just be something at the retailer(wallet) side that prevents over spends. there should be something deeper at the pool/network level that realises that something has gone wrong.

though i still oppose the dire need of transaction fee's to suppliment the block reward(for atleast a decade), those that do want to pay a fee should still be protected from making mistakes. EG. if fee is $1+(0.0025+), then nodes shouldnt relay it. same for miners if fee is $1 (>0.0025) then dont add to block.

that way people can still pay 4cents. or if stupid upto $1 in a race for priority.. but anything more is an obvious mistake especially a $6000 fee.