It's not just the score thing, it's up to the point

that you can have a comfortable feeling that they will pay you the rent on time and in full. You need to figure out that they don't have any collections from previous landlords, that's the most important. You also need to ensure that they didn't get evicted before (from checking Eviction Report with additional cost). Occasional credit card late payment may be okay as long as they have paid up up to now. Ask them why they paid late on credit card. If it was only short term cash flow issue, they explained it well. It may not be a long term issue. Reading a credit report is like reading a person's resume, you want to get a feeling. Credit score is not an absolute criterion.