Few, if any, lenders would be willing to give guaranteed approval for a bad credit personal loan. Borrowers with bad credit histories can have more complicated financial circumstances than other borrowers, so lenders will want time to study your application.
It’s all about risk. When someone applies for a personal loan, the lender evaluates how likely that borrower would be to repay the money. Lenders are more willing to give personal loans to borrowers with good credit than bad credit, because there’s a higher likelihood that the personal loan will be repaid.
So a borrower with good credit is more likely to have a loan approved and to get that approval faster, while a borrower with bad credit is less likely to have a loan approved and to get that approval slower.