Bad credit is generally considered a FICO score of 590 or less. It's easy to qualify for a payday loan because there are no credit check requirements on short term cash advances. Proof of income and employment history is all you need to qualify. Short term lending is not a viable long term solution for managing debt, but for brief periods can be utilized effectively during times of financial instability.
Paying bills in full and on time gives your credit score a boost, so a cash advance may actually help keep your hard earned credit history in tact. Having bad credit will usually limit your ability to get a loan from traditional financial institutions, but some lenders do offer fixed rate installment loans to bad credit borrowers.