You're primarily focusing on small business, that's great. It brings social values as well as economic. There used to be a lot more private family businesses in EU. Now many of them are fading away for many reasons. Perhaps with costs optimization and the trust rate solution thay will thrive again.
What happends if a company paid for a guarantee from another user and then fails to provide the needed quality?
The guaranteeing business gives a time-constrained guarantee to the asking business by staking its own trust rank. All changes (positive or negative) to the trust rank of the requesting business are immediately reflected in the trust rank of the guaranteer. I suggest you take a look at our whitepaper on page 23: https://procurean.network/whitepaper
hopefully that will be a strong argument against the fraud.