Purchasing a business. Bitcoin Vs bank transfer Vs cash

I am purchasing a small business. The agreed price is around 1btc. The government does not allow me to purchase anything legally with bitcoin.

To make a bank transfer, I will have to transfer a portion of savings to my current account, transfer that to my local bank with conversion to the currency here, and then transfer the amount to the seller. This means two bank to bank transfer fees, and an exchange fee. Then seller has a 15% tax to pay the government.

To pay in cash I have the added step of arranging with my local bank to allow me to collect that amount of cash on a specific day, then have to carry that cash with me to a notary, where documents can be signed, cash transferred, and ownership of the business transferred. The seller then had to carry a backpack full of cash through the city to their bank and deposit it.

Bitcoin. We meet the seller at a notary. Seller gives me the wallet address. I send. Notary confirms transaction. Business is signed over. We all go for coffee.

Considering the seller is also pro bitcoin. What is stopping them from selling me the business for 1£$¥€¢ or whatever. Then me transferring 1 BTC whilst we sit in the cafe with our coffees?

It's madness.