Good credit is absolutely required for an unsecured loan.  A few blemishes are okay for other loans provided that they are paid off prior to settlement.  

Defaults to other finance companies will generally lead to a decline unless they were paid some time ago.

If there has been a liquidation or a recievership in a borrowers past a loan may still be considered provided the loan is not ongoing.

Ex-bankrupts that are proving their worth can be considered.

Invoice finance, secured loans and guarantor loans are best suited to borrowers with a blemished credit history.