TAXES
Original purchases can be made in Tether.
this is not a solution it is a disaster. because tether is not a good choice ever.
first of all you said there is no "paper trail" but when you use crypto you just cut the bank, but you are still making a trade and it is registered somewhere!
WARRANTY
for this you just have to change the rules of the contracts if you are worried about the volatility. for example lets say the car is worth $1000 today you get paid 0.125
BTC at bitcoin price of $8000 and tomorrow price of bitcoin goes to $100,000 and the contract simply says it will be the USD value taken from coinbase so you pay back 0.01
BTCeverything solved!
you see when you want to accept a new form of payment, everything will come down to the rules that the two parties agree about in the contract. you think ahead and set these rules and you both sign them.