Fair Isaac or FICO scores are the key to the lock that must be opened before any bank will entertain any loan for your clients. Before deciding on what terms they will offer a loan (which they base on their "risk"), lenders want to know two things about the ability to pay back the loan, and the willingness to pay back the loan.

For the first, they look at income-to-debt obligation ratio. For the willingness to pay back the loan, they consult the credit score.
The most widely used credit scores are FICO scores, which were developed by Fair Isaac & Company, Inc. (and they're named after their inventor!). Your FICO score is between 350 (high risk) and 850 (low risk).
Credit scores only consider the information contained in the credit profile. They do not consider income, savings, down payment amount, or demographic factors like gender, race, nationality or marital status.  

Credit scoring was developed as a way to consider only what was relevant to somebody's willingness to repay the loan.

Different portions of the credit history are given different weights. Thirty-five percent of FICO score is based on specific payment history. Thirty percent is current level of indebtedness. Fifteen percent each is the time open credit has been in use (ten years old accounts are good, six month old ones aren't as good) and types of credit available to you (installment loans such as student loans, car loans, etc. versus revolving and debit accounts like credit cards). Finally, five percent is pursuit of new credit -- credit scores requested.

Credit analysis: The SBA credit analysis and credit decision processes are delegated to the lender. However, the lender is required to use appropriate and generally accepted credit analysis processes and procedures, and these procedures must be consistent with those used for its non-SBA guaranteed commercial loans.

Acceptable analytical processes include “credit scoring,” if the lender uses credit scoring for non-SBA guaranteed commercial loans.  SBA assumes that the Lender’s decision to seek SBA’s guaranty is made after the lender has conducted a thorough credit analysis of the applicant’s request for financial assistance in accordance with prudent lending practices.

No loan can be guaranteed by SBA unless there is the reasonable assurance of repayment in a timely manner. The Lender’s written credit analysis must demonstrate at a minimum a thorough assessment of 1) repayment ability; 2) financial statement analysis including ratio, trend, and pro forma analysis; 3) management capabilities; 4) collateral coverage; and 5) lender’s experience with the applicant.