How to use smart contracts for guarantor transactions?

[ilovebtceth]

I do not quite understand how to use them and how to negotiate the terms of the transaction? Many times I used the guarantor services for ordinary currencies, and there you can negotiate the terms of the transaction to complete the transaction. How to do it with smart contracts?
Why was my topic moved to this section? I asked not about ordinary currencies, and certainly not about altcoin, but about bitcoin!